Exhibit 99.1 Closing In On Cancer September 2020Exhibit 99.1 Closing In On Cancer September 2020

Disclaimer This presentation (including any oral commentary that accompanies this marketable drugs; potential adverse public reaction to the use of cancer presentation) contains forward-looking statements within the meaning of immunotherapies; potential delays in enrollment of patients, which could the Private Securities Litigation Reform Act of 1995. All statements affect the receipt of necessary regulatory approvals; failure to obtain contained in this presentation that do not relate to matters of historical marketing approval internationally; failure to compete successfully against fact should be considered forward-looking statements, including without other drug companies; potential competition from other drug companies limitation statements regarding the impact our Biclonics® platform can if we fail to obtain orphan drug designation or maintain orphan drug have on cancer, our product candidates' potential to treat certain types of exclusivity for our products; our reliance on third parties to conduct our tumors, the timing of regulatory filings and the timing and anticipated clinical trials and the potential for those third parties to not perform data read outs or results from our clinical trials and our collaborations. satisfactorily; our reliance on third parties to manufacture our product These forward-looking statements are based on management's current candidates, which may delay, prevent or impair our development and expectations. These statements are neither promises nor guarantees, but commercialization efforts; protection of our proprietary technology; our involve known and unknown risks, uncertainties and other important patents being found invalid or unenforceable; potential lawsuits for factors that may cause our actual results, performance or achievements to infringement of third-party intellectual property; our ability to attract and be materially different from any future results, performance or retain key personnel; managing our growth could result in difficulties; and achievements expressed or implied by the forward-looking statements, we may lose our foreign private issuer status and incur significant including, but not limited to, the following: we have incurred significant expenses as a result. losses, are not currently profitable and may never become profitable; our These and other important factors discussed under the caption “Risk need for additional funding, which may not be available and which may Factors” in our in our Quarterly Report on Form 10-Q for the quarterly require us to restrict out operations or require us to relinquish rights to period ended June 30, 2020 filed with the Securities and Exchange our technologies or bispecific antibody candidates; potential delays in Commission, or SEC, on August 6, 2020, and our other reports filed with regulatory approval and impacts of the COVID-19 pandemic, which would the SEC, could cause actual results to differ materially from those impact our ability to commercialize our product candidates and affect our indicated by the forward-looking statements made in this presentation. ability to generate revenue; the unproven approach to therapeutic Any such forward-looking statements represent management's estimates TM intervention of our Biclonics®, and Triclonics technology; our limited as of the date of this presentation. While we may elect to update such operating history; economic, political, regulatory and other risks involved forward-looking statements at some point in the future, we disclaim any with international operations; the lengthy and expensive process of obligation to do so, even if subsequent events cause our views to change. clinical drug development, which has an uncertain outcome; the unpredictable nature of our early stage development efforts for 2Disclaimer This presentation (including any oral commentary that accompanies this marketable drugs; potential adverse public reaction to the use of cancer presentation) contains forward-looking statements within the meaning of immunotherapies; potential delays in enrollment of patients, which could the Private Securities Litigation Reform Act of 1995. All statements affect the receipt of necessary regulatory approvals; failure to obtain contained in this presentation that do not relate to matters of historical marketing approval internationally; failure to compete successfully against fact should be considered forward-looking statements, including without other drug companies; potential competition from other drug companies limitation statements regarding the impact our Biclonics® platform can if we fail to obtain orphan drug designation or maintain orphan drug have on cancer, our product candidates' potential to treat certain types of exclusivity for our products; our reliance on third parties to conduct our tumors, the timing of regulatory filings and the timing and anticipated clinical trials and the potential for those third parties to not perform data read outs or results from our clinical trials and our collaborations. satisfactorily; our reliance on third parties to manufacture our product These forward-looking statements are based on management's current candidates, which may delay, prevent or impair our development and expectations. These statements are neither promises nor guarantees, but commercialization efforts; protection of our proprietary technology; our involve known and unknown risks, uncertainties and other important patents being found invalid or unenforceable; potential lawsuits for factors that may cause our actual results, performance or achievements to infringement of third-party intellectual property; our ability to attract and be materially different from any future results, performance or retain key personnel; managing our growth could result in difficulties; and achievements expressed or implied by the forward-looking statements, we may lose our foreign private issuer status and incur significant including, but not limited to, the following: we have incurred significant expenses as a result. losses, are not currently profitable and may never become profitable; our These and other important factors discussed under the caption “Risk need for additional funding, which may not be available and which may Factors” in our in our Quarterly Report on Form 10-Q for the quarterly require us to restrict out operations or require us to relinquish rights to period ended June 30, 2020 filed with the Securities and Exchange our technologies or bispecific antibody candidates; potential delays in Commission, or SEC, on August 6, 2020, and our other reports filed with regulatory approval and impacts of the COVID-19 pandemic, which would the SEC, could cause actual results to differ materially from those impact our ability to commercialize our product candidates and affect our indicated by the forward-looking statements made in this presentation. ability to generate revenue; the unproven approach to therapeutic Any such forward-looking statements represent management's estimates TM intervention of our Biclonics®, and Triclonics technology; our limited as of the date of this presentation. While we may elect to update such operating history; economic, political, regulatory and other risks involved forward-looking statements at some point in the future, we disclaim any with international operations; the lengthy and expensive process of obligation to do so, even if subsequent events cause our views to change. clinical drug development, which has an uncertain outcome; the unpredictable nature of our early stage development efforts for 2

Merus Overview Oncology-focused Company Developing Multispecific Antibody Therapies Bispecific and trispecific cancer therapeutic candidates based on the human IgG format Established Clinical Pipeline Clinical proof-of-concept with zenocutuzumab (“Zeno”) in patients with neuregulin 1 (NRG1) positive gene fusion (NRG1+) cancers Near Term Data Readouts and Strong Cash Position into 2H 2022 Zeno NRG-1 phase 1/2 clinical data 2Q 2021 Leading Multispecific Antibody (Multiclonics®) Platforms Common light chain format permits broad high throughput Biclonics® and Triclonics™ discovery Strategic Collaborations to Unlock Platform Value Multiple strategic collaborations and license agreements 3Merus Overview Oncology-focused Company Developing Multispecific Antibody Therapies Bispecific and trispecific cancer therapeutic candidates based on the human IgG format Established Clinical Pipeline Clinical proof-of-concept with zenocutuzumab (“Zeno”) in patients with neuregulin 1 (NRG1) positive gene fusion (NRG1+) cancers Near Term Data Readouts and Strong Cash Position into 2H 2022 Zeno NRG-1 phase 1/2 clinical data 2Q 2021 Leading Multispecific Antibody (Multiclonics®) Platforms Common light chain format permits broad high throughput Biclonics® and Triclonics™ discovery Strategic Collaborations to Unlock Platform Value Multiple strategic collaborations and license agreements 3

Merus Multiclonics® Bispecific and Trispecific Cancer Therapeutic Candidates in Human Monoclonal Antibody Formats • Large-scale screening to select from up to 1,000s of candidates • Potential to identify best and new biological combinations • Fully human IgG format allows for: • Ease of manufacturing • Low immunogenicity risk • Predictable in vivo behavior • Durable, consistent half life • Potential for ADCC enhancement and Fc silencing • Robust IP portfolio: patents covering Multiclonics® technology, including common light chain antibody generation and dimerization by charge engineering 4Merus Multiclonics® Bispecific and Trispecific Cancer Therapeutic Candidates in Human Monoclonal Antibody Formats • Large-scale screening to select from up to 1,000s of candidates • Potential to identify best and new biological combinations • Fully human IgG format allows for: • Ease of manufacturing • Low immunogenicity risk • Predictable in vivo behavior • Durable, consistent half life • Potential for ADCC enhancement and Fc silencing • Robust IP portfolio: patents covering Multiclonics® technology, including common light chain antibody generation and dimerization by charge engineering 4

Merus Clinical Pipeline BISPECIFIC PROGRAM TARGETS INDICATION(S) PRECLINICAL PHASE 1 PHASE 1/2 STATUS Phase 1/2 trial ongoing NRG1+ Pancreatic Zenocutuzumab (Zeno) NRG1+ Lung HER3 x HER2 Clinical data and program (MCLA-128) NRG1+ Other solid tumors update planned 2Q 2021 Phase 1 Trial Ongoing MCLA-158 Lgr5 x EGFR Solid tumors Update planned YE 2020 (ex- U.S.) MCLA-145 CD137 x PD-L1 Solid tumors Phase 1 Trial Ongoing IND Enabling (China) MCLA-129 EGFR x c-MET Solid tumors Studies Ongoing ONO-4685* Autoimmune disease Phase 1 Trial Ongoing PD-1 x CD3 ….* Autoimmune disease Undisclosed * If commercialized, Merus to receive royalties 5Merus Clinical Pipeline BISPECIFIC PROGRAM TARGETS INDICATION(S) PRECLINICAL PHASE 1 PHASE 1/2 STATUS Phase 1/2 trial ongoing NRG1+ Pancreatic Zenocutuzumab (Zeno) NRG1+ Lung HER3 x HER2 Clinical data and program (MCLA-128) NRG1+ Other solid tumors update planned 2Q 2021 Phase 1 Trial Ongoing MCLA-158 Lgr5 x EGFR Solid tumors Update planned YE 2020 (ex- U.S.) MCLA-145 CD137 x PD-L1 Solid tumors Phase 1 Trial Ongoing IND Enabling (China) MCLA-129 EGFR x c-MET Solid tumors Studies Ongoing ONO-4685* Autoimmune disease Phase 1 Trial Ongoing PD-1 x CD3 ….* Autoimmune disease Undisclosed * If commercialized, Merus to receive royalties 5

Zenocutuzumab Promising early clinical activity MCLA-128 or “Zeno” in patients with NRG1+ cancers HER2 x HER3 bispecific HER3 • NRG-1 positive gene fusions (NRG1+) are rare genetic target events occurring in lung, pancreatic and other solid tumors • Unique DOCK & BLOCK® mechanism of Zeno potently inhibits NRG1+-driven tumor growth HER2 target • Enhanced ADCC mediates tumor elimination by cancer immune effector cells cell • eNRGy Trial enrolling and Early Access Program ongoing • Clinical data and program update expected 2Q 2021 6Zenocutuzumab Promising early clinical activity MCLA-128 or “Zeno” in patients with NRG1+ cancers HER2 x HER3 bispecific HER3 • NRG-1 positive gene fusions (NRG1+) are rare genetic target events occurring in lung, pancreatic and other solid tumors • Unique DOCK & BLOCK® mechanism of Zeno potently inhibits NRG1+-driven tumor growth HER2 target • Enhanced ADCC mediates tumor elimination by cancer immune effector cells cell • eNRGy Trial enrolling and Early Access Program ongoing • Clinical data and program update expected 2Q 2021 6

Zeno DOCK & BLOCK® Mechanism of Action Uniquely Suited to Target NRG1+ Cancers Zeno Blocks Tumor Growth in NRG1+ PDX Model Tumor Volume 3 (mm ) DOCKS BLOCKS to HER2 on tumor HER3 signaling even 1400 Control Zeno cells to efficiently in high NRG1+ tumor 1200 Zeno block HER2:HER3 environments 1000 dimer formation + 800 Enhanced ADCC then mediates tumor 600 elimination by 400 immune killer cells 200 0 1 8 15 22 29 Study Day Zeno blocks tumor cell growth and survival driven by HER3 ligands, including neuregulin (NRG-1) or NRG-1 positive gene fusions (NRG1+) 7 Source: Geuijen C et al. Cancer Cell (2018) https://www.cell.com/cancer-cell/fulltext/S1535-6108(18)30174-0#%20Zeno DOCK & BLOCK® Mechanism of Action Uniquely Suited to Target NRG1+ Cancers Zeno Blocks Tumor Growth in NRG1+ PDX Model Tumor Volume 3 (mm ) DOCKS BLOCKS to HER2 on tumor HER3 signaling even 1400 Control Zeno cells to efficiently in high NRG1+ tumor 1200 Zeno block HER2:HER3 environments 1000 dimer formation + 800 Enhanced ADCC then mediates tumor 600 elimination by 400 immune killer cells 200 0 1 8 15 22 29 Study Day Zeno blocks tumor cell growth and survival driven by HER3 ligands, including neuregulin (NRG-1) or NRG-1 positive gene fusions (NRG1+) 7 Source: Geuijen C et al. Cancer Cell (2018) https://www.cell.com/cancer-cell/fulltext/S1535-6108(18)30174-0#%20

Zeno Safety Profile for Single Agent Use Safety Data in Over 100 Patients in Phase 1/2 Trials Safety and Tolerability in Phase 1/2 Trial OVER 100 PATIENTS EVALUATED* Zeno Dosing: 750 mg ranging from q1w-q3w • Single agent well tolerated • Low risk for immunogenicity • Most AEs were grade 1-2 Data cut off: Jan-2019. Refer to https://merus.nl/publications/ for full data presented. Refer to ASCO poster 2018 and AACR-NCI-EORTC International Conference on 8 Molecular Targets and Cancer Therapeutics 2019 https://merus.nl/app/uploads/2019/10/AACR-NCI-EORTC_Poster-LB-B12_NRG1-MCLA-128_10252019_FINAL.pdfZeno Safety Profile for Single Agent Use Safety Data in Over 100 Patients in Phase 1/2 Trials Safety and Tolerability in Phase 1/2 Trial OVER 100 PATIENTS EVALUATED* Zeno Dosing: 750 mg ranging from q1w-q3w • Single agent well tolerated • Low risk for immunogenicity • Most AEs were grade 1-2 Data cut off: Jan-2019. Refer to https://merus.nl/publications/ for full data presented. Refer to ASCO poster 2018 and AACR-NCI-EORTC International Conference on 8 Molecular Targets and Cancer Therapeutics 2019 https://merus.nl/app/uploads/2019/10/AACR-NCI-EORTC_Poster-LB-B12_NRG1-MCLA-128_10252019_FINAL.pdf

Size Zeno Clinical Response in NRG1+ Cancers Patient Data Presented at 2019 AACR-NCI-EORTC International Conference Example pancreatic cancer patient: As of Oct. 2019, 7+ months MCLA-128, 750 mg IV, q2w Maximal related toxicity ≤ grade 2 300 0 -10 CA 19-9 250 -20 RECIST (%change from baseline) -30 200 -40 150 -50 -44% ↓ -60 100 -54% ↓ -70 -80 50 -90 0 -100 0 4 8 12 16 20 24 28 32 Weeks Source: AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics 2019 9 https://merus.nl/app/uploads/2019/10/AACR-NCI-EORTC_Poster-LB-B12_NRG1-MCLA-128_10252019_FINAL.pdf/ CA19-9Size Zeno Clinical Response in NRG1+ Cancers Patient Data Presented at 2019 AACR-NCI-EORTC International Conference Example pancreatic cancer patient: As of Oct. 2019, 7+ months MCLA-128, 750 mg IV, q2w Maximal related toxicity ≤ grade 2 300 0 -10 CA 19-9 250 -20 RECIST (%change from baseline) -30 200 -40 150 -50 -44% ↓ -60 100 -54% ↓ -70 -80 50 -90 0 -100 0 4 8 12 16 20 24 28 32 Weeks Source: AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics 2019 9 https://merus.nl/app/uploads/2019/10/AACR-NCI-EORTC_Poster-LB-B12_NRG1-MCLA-128_10252019_FINAL.pdf/ CA19-9

Zeno Activity and Promising Durability Observed in Patients Zeno NRG1+ Clinical Activity Reported by MSKCC at 2019 AACR-NCI-EORTC International Conference PANCREATIC CANCER LUNG CANCER Tumor size reduction 41% (PR) 54% (PR) 25% (SD) PET scan nd Neg Neg Decline in tumor marker ~75% ~90% N/A Duration of treatment (mo) >7* >7* ~ 5* Source: AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics 2019 https://merus.nl/app/uploads/2019/10/AACR-NCI-EORTC_Poster-LB-B12_NRG1-MCLA-128_10252019_FINAL.pdf Overall Experience with Zeno in NRG1+ Tumors as of October 2019 N PANCREATIC CANCER LUNG CANCER Evaluable 6 PR 7 mo*; SD 7 mo PR 5 mo*; SD 7 mo; PD; PD Died of progressive disease Non-evaluable 3 2 Pts not yet at first evaluation prior to first evaluation 5 patients enrolled on the eNRGy trial; 4 patients treated under Early Access Program Source: Merus Press Release Oct 27, 2019 https://ir.merus.nl/news-releases/news-release-details/merus-bispecific-antibody-mcla-128-shows-encouraging-early *Indicates treatment was ongoing at the time of the conference; nd, no data; N/A, not applicable 10Zeno Activity and Promising Durability Observed in Patients Zeno NRG1+ Clinical Activity Reported by MSKCC at 2019 AACR-NCI-EORTC International Conference PANCREATIC CANCER LUNG CANCER Tumor size reduction 41% (PR) 54% (PR) 25% (SD) PET scan nd Neg Neg Decline in tumor marker ~75% ~90% N/A Duration of treatment (mo) >7* >7* ~ 5* Source: AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics 2019 https://merus.nl/app/uploads/2019/10/AACR-NCI-EORTC_Poster-LB-B12_NRG1-MCLA-128_10252019_FINAL.pdf Overall Experience with Zeno in NRG1+ Tumors as of October 2019 N PANCREATIC CANCER LUNG CANCER Evaluable 6 PR 7 mo*; SD 7 mo PR 5 mo*; SD 7 mo; PD; PD Died of progressive disease Non-evaluable 3 2 Pts not yet at first evaluation prior to first evaluation 5 patients enrolled on the eNRGy trial; 4 patients treated under Early Access Program Source: Merus Press Release Oct 27, 2019 https://ir.merus.nl/news-releases/news-release-details/merus-bispecific-antibody-mcla-128-shows-encouraging-early *Indicates treatment was ongoing at the time of the conference; nd, no data; N/A, not applicable 10

Zeno Clinical Programs in NRG1+ Cancers eNRGy Clinical Trial and Early Access Program Ongoing Early Access Program Pancreatic Cancer • Phase 1/2 global single arm trial • For eligible patients who do not of Zeno in NRG1+ cancers enroll on the eNRGy trial • Cohorts include Pancreatic, NSCLC, • Allows patients with NRG1+ cancers and other solid tumors to receive treatment with Zeno NSCLC • Majority of clinical trial sites open • Evaluations and patient follow up and enrolling may be similar to eNRGy protocol • Ongoing Phase 1/2 trial update • May provide additional clinical data expected 2Q 2021 in support of Zeno NRG1+ program Other Solid Tumors 11Zeno Clinical Programs in NRG1+ Cancers eNRGy Clinical Trial and Early Access Program Ongoing Early Access Program Pancreatic Cancer • Phase 1/2 global single arm trial • For eligible patients who do not of Zeno in NRG1+ cancers enroll on the eNRGy trial • Cohorts include Pancreatic, NSCLC, • Allows patients with NRG1+ cancers and other solid tumors to receive treatment with Zeno NSCLC • Majority of clinical trial sites open • Evaluations and patient follow up and enrolling may be similar to eNRGy protocol • Ongoing Phase 1/2 trial update • May provide additional clinical data expected 2Q 2021 in support of Zeno NRG1+ program Other Solid Tumors 11

Identifying and Recruiting NRG1+ Patients NRG1+ Cancers are Found Across Comprehensive Effort to Identify Multiple Solid Tumor Types and Recruit NRG1+ Patients ESTIMATED TUMOR TYPE INCIDENCE (%) IDENTIFICATION COLLABORATION PLACEMENT Patient testing and Physician, trial site Patient logistics / LUNG 0.3 – 3.0 physician engagement engagement & support support for eNRGy campaigns 1-833-NRG-1234 trial or EAP www.nrg1.com PANCREAS 0.5 – 1.5 OTHER < 1.0 Early Access Program Note: Projections of NRG1+ estimated incidence based on limited published information, including Jonna S et al. Clinical Cancer Research (2019); independent epidemiology review https://ir.merus.nl/news-releases/news-release-details/merus-announces-acceptance-six-abstracts-upcoming-medical; and Wang (2015); Duruisseaux (2017); Trombetta (2018); McCoach (2018); 12 Karlsson (2019); Drilon (2018); Fernandez-Cuesta (2014); Seto (2018); and Scheel (2015) Identifying and Recruiting NRG1+ Patients NRG1+ Cancers are Found Across Comprehensive Effort to Identify Multiple Solid Tumor Types and Recruit NRG1+ Patients ESTIMATED TUMOR TYPE INCIDENCE (%) IDENTIFICATION COLLABORATION PLACEMENT Patient testing and Physician, trial site Patient logistics / LUNG 0.3 – 3.0 physician engagement engagement & support support for eNRGy campaigns 1-833-NRG-1234 trial or EAP www.nrg1.com PANCREAS 0.5 – 1.5 OTHER < 1.0 Early Access Program Note: Projections of NRG1+ estimated incidence based on limited published information, including Jonna S et al. Clinical Cancer Research (2019); independent epidemiology review https://ir.merus.nl/news-releases/news-release-details/merus-announces-acceptance-six-abstracts-upcoming-medical; and Wang (2015); Duruisseaux (2017); Trombetta (2018); McCoach (2018); 12 Karlsson (2019); Drilon (2018); Fernandez-Cuesta (2014); Seto (2018); and Scheel (2015)

Designed to potently block signaling MCLA-158 and growth in Wnt-dysregulated Lgr5 x EGFR bispecific solid tumors Lgr5 • Binds to EGFR and Lgr5, an intestinal cancer- target initiating cell antigen • Potential to address significant unmet need in colorectal cancers and a variety of other solid tumors EGFR target • Blocks growth in Wnt-dysregulated tumor models cancer mut including Ras cell • Modifications to enhance ADCC • Phase 1 trial update planned for year end 2020 13Designed to potently block signaling MCLA-158 and growth in Wnt-dysregulated Lgr5 x EGFR bispecific solid tumors Lgr5 • Binds to EGFR and Lgr5, an intestinal cancer- target initiating cell antigen • Potential to address significant unmet need in colorectal cancers and a variety of other solid tumors EGFR target • Blocks growth in Wnt-dysregulated tumor models cancer mut including Ras cell • Modifications to enhance ADCC • Phase 1 trial update planned for year end 2020 13

MCLA-158 — Novel Target and Innovative MoA Superior Growth Inhibition and Selectivity of Tumor Versus Healthy Tissue Superior SELECTIVITY for Superior ACTIVITY ONGOING PHASE 1 TRIAL tumor-derived organoids compared to Cetuximab T u m o r C o l o n p t C 5 5 N o r m a l C o l o n p t C 5 5 Organoid 1 5 0 M C L A 1 5 8 C 5 5 T M C L A 1 5 8 C 5 5 N No antibody Tumor Colon % Survival Size C e t u x i m a b C 5 5 T C e t u x i m a b C 5 5 N Cetuximab • Global Phase 1 dose Cetuximab MCLA-158 1 0 0 100 MCLA-158 escalation and cohort 1 0 0 100 expansion trial Normal Colon Cetuximab MCLA-158 50 5 0 5 0 P = 0 . 0 0 0 1 50• Protocol includes dose expansion phase at RP2D > 100-fold P=0.0001 0 0 • Update planned year end 0 0 - 3 - 2 - 1 0 1 2 0 1 0 2 0 3 0 -3 -3 -1 0 1 2 0 10 20 30 D o s e ( l o gm g / m l ) 2020 D a y s e l a p s e d Days Elapsed Dose (log µg/ml) • Activity observed in xenograft models resistant to treatment with Cetuximab • MCLA-158 discriminated between organoids derived from tumor and healthy tissue 14 Source: Rob C. Roovers (ASCO 2017 Poster Presentation) )https://merus.nl/app/uploads/2019/02/MCLA-158-poster-AACR2017.pdf P e r c e n t s u r v i v a l N o r m a l i z e d T u m o r o i d s i z eMCLA-158 — Novel Target and Innovative MoA Superior Growth Inhibition and Selectivity of Tumor Versus Healthy Tissue Superior SELECTIVITY for Superior ACTIVITY ONGOING PHASE 1 TRIAL tumor-derived organoids compared to Cetuximab T u m o r C o l o n p t C 5 5 N o r m a l C o l o n p t C 5 5 Organoid 1 5 0 M C L A 1 5 8 C 5 5 T M C L A 1 5 8 C 5 5 N No antibody Tumor Colon % Survival Size C e t u x i m a b C 5 5 T C e t u x i m a b C 5 5 N Cetuximab • Global Phase 1 dose Cetuximab MCLA-158 1 0 0 100 MCLA-158 escalation and cohort 1 0 0 100 expansion trial Normal Colon Cetuximab MCLA-158 50 5 0 5 0 P = 0 . 0 0 0 1 50• Protocol includes dose expansion phase at RP2D > 100-fold P=0.0001 0 0 • Update planned year end 0 0 - 3 - 2 - 1 0 1 2 0 1 0 2 0 3 0 -3 -3 -1 0 1 2 0 10 20 30 D o s e ( l o gm g / m l ) 2020 D a y s e l a p s e d Days Elapsed Dose (log µg/ml) • Activity observed in xenograft models resistant to treatment with Cetuximab • MCLA-158 discriminated between organoids derived from tumor and healthy tissue 14 Source: Rob C. Roovers (ASCO 2017 Poster Presentation) )https://merus.nl/app/uploads/2019/02/MCLA-158-poster-AACR2017.pdf P e r c e n t s u r v i v a l N o r m a l i z e d T u m o r o i d s i z e

Designed to recruit and activate MCLA-145 tumor infiltrating T-cells PD-L1 x CD137 bispecific PD-L1 • Binds to PD-L1 on tumor cells and CD137 target (4-1BB), a potent activator of tumor infiltrating T-cells, on activated T-cells cancer • Targeting to PD-L1 positive cells in the tumor cell and blocking the PD-1/PD-L1 inhibitory signal CD137 target • Potential in a variety of solid tumors and hematological malignancies immune • Global phase 1 trial ongoing in collaboration cell with Incyte 15Designed to recruit and activate MCLA-145 tumor infiltrating T-cells PD-L1 x CD137 bispecific PD-L1 • Binds to PD-L1 on tumor cells and CD137 target (4-1BB), a potent activator of tumor infiltrating T-cells, on activated T-cells cancer • Targeting to PD-L1 positive cells in the tumor cell and blocking the PD-1/PD-L1 inhibitory signal CD137 target • Potential in a variety of solid tumors and hematological malignancies immune • Global phase 1 trial ongoing in collaboration cell with Incyte 15

MCLA-145 — Targets PD-L1 Positive Tumor Cells Demonstrated Potent T Cell Activation in Preclinical Studies Primary T Cell Transactivation Assay Ongoing Phase 1 Trial [IL-2] (pg/mL) MCLA-145 5000 ˄ CD137mAb • Global open-label Phase 1 dose ˄ CD137mAb escalation trial ongoing 4000 * PD-L1mAb x Neg Ctrl Ab • Clinical trial co-developed 3000 ^ Urelumab Analog in collaboration with * Atezolizumab Analog Incyte Corporation 2000 1000 0 x x x x x x 1 4 -1 0 2 3 5 10 10 10 10 10 10 10 IgG Concentration (ng/mL) Source: 2019 AACR Presentation A bispecific Fc-silenced IgG1 antibody (MCLA-145) requires PD-L1 binding to activate CD137 16 https://merus.nl/app/uploads/2019/04/IC171-19E-AACR19-Mayes-MCLA-145-MoA-Poster_MT06_for-approval-032019.pdfMCLA-145 — Targets PD-L1 Positive Tumor Cells Demonstrated Potent T Cell Activation in Preclinical Studies Primary T Cell Transactivation Assay Ongoing Phase 1 Trial [IL-2] (pg/mL) MCLA-145 5000 ˄ CD137mAb • Global open-label Phase 1 dose ˄ CD137mAb escalation trial ongoing 4000 * PD-L1mAb x Neg Ctrl Ab • Clinical trial co-developed 3000 ^ Urelumab Analog in collaboration with * Atezolizumab Analog Incyte Corporation 2000 1000 0 x x x x x x 1 4 -1 0 2 3 5 10 10 10 10 10 10 10 IgG Concentration (ng/mL) Source: 2019 AACR Presentation A bispecific Fc-silenced IgG1 antibody (MCLA-145) requires PD-L1 binding to activate CD137 16 https://merus.nl/app/uploads/2019/04/IC171-19E-AACR19-Mayes-MCLA-145-MoA-Poster_MT06_for-approval-032019.pdf

Interim phase 1 trial results of MCLA-117 novel T-cell engager at EHA 2020 CLEC12A x CD3 bispecific CLEC12A • Designed with lower CD3 affinity binding to potentially target reduce the risk of cytokine release syndrome • Acceptable safety profile in clinical trial • Active in acute myeloid leukemia (AML) with T-cell cancer activation, cytokine elevation and AML blast reductions cell in some patients CD3 target • Insufficient clinical activity in escalation to continue to enroll dose expansion cohorts • Findings from this trial expected to inform further immune development of our extensive proprietary T-cell cell engager platform 17Interim phase 1 trial results of MCLA-117 novel T-cell engager at EHA 2020 CLEC12A x CD3 bispecific CLEC12A • Designed with lower CD3 affinity binding to potentially target reduce the risk of cytokine release syndrome • Acceptable safety profile in clinical trial • Active in acute myeloid leukemia (AML) with T-cell cancer activation, cytokine elevation and AML blast reductions cell in some patients CD3 target • Insufficient clinical activity in escalation to continue to enroll dose expansion cohorts • Findings from this trial expected to inform further immune development of our extensive proprietary T-cell cell engager platform 17

Designed to target lung cancer MCLA-129 and other solid tumors c-MET x EGFR Bispecific c-Met target • Targets both c-Met and EGFR on cancer cells as well as resistance mechanism • Preclinical program directed at a target- pair combination with clinical validation EGFR target • Significant opportunity in lung cancer cancer and other solid tumors cell 18Designed to target lung cancer MCLA-129 and other solid tumors c-MET x EGFR Bispecific c-Met target • Targets both c-Met and EGFR on cancer cells as well as resistance mechanism • Preclinical program directed at a target- pair combination with clinical validation EGFR target • Significant opportunity in lung cancer cancer and other solid tumors cell 18

Merus Collaborations & Licensing Agreements Expanding Merus pipeline through development of innovative therapeutics Global collaboration MCLA-129 Collaboration with Biclonics® Licensing of up to 11 Biclonics® EGFR x C-MET 3 immuno-oncology Agreement for Auto- programs collaboration Biclonics® programs immune diseases Betta conducting Simcere responsible for Phase 1 trial in Japan for $200mm at signing and IND-enabling studies; IND-enabling and China ONO-4685, a PD-1 x CD3 research funding, Merus Merus retains global studies; Merus retains bispecific antibody retains full U.S. rights to develop, commercialize rights ex-China global rights ex-China MCLA-145 19Merus Collaborations & Licensing Agreements Expanding Merus pipeline through development of innovative therapeutics Global collaboration MCLA-129 Collaboration with Biclonics® Licensing of up to 11 Biclonics® EGFR x C-MET 3 immuno-oncology Agreement for Auto- programs collaboration Biclonics® programs immune diseases Betta conducting Simcere responsible for Phase 1 trial in Japan for $200mm at signing and IND-enabling studies; IND-enabling and China ONO-4685, a PD-1 x CD3 research funding, Merus Merus retains global studies; Merus retains bispecific antibody retains full U.S. rights to develop, commercialize rights ex-China global rights ex-China MCLA-145 19

Our Platform – Unparalleled Capabilities in Multispecific Antibodies Empiric selection of best candidates from hundreds of different Biclonics® against two different targets Patented discovery Proprietary inventory Robotics generate In-format, unbiased functional engine including the of thousands of cLC thousands of Multiclonics® screening with high “Merus Mouse” antibodies, each with for functional screening throughput cellular assays (MeMo®) generates distinct purposes and diverse, high quality unique features CH3 domain variations “DEKK” drives preferential, common light chain efficient pairing of different antibody chains to (cLC) antibody panels create multispecific functionality Our Platform – Unparalleled Capabilities in Multispecific Antibodies Empiric selection of best candidates from hundreds of different Biclonics® against two different targets Patented discovery Proprietary inventory Robotics generate In-format, unbiased functional engine including the of thousands of cLC thousands of Multiclonics® screening with high “Merus Mouse” antibodies, each with for functional screening throughput cellular assays (MeMo®) generates distinct purposes and diverse, high quality unique features CH3 domain variations “DEKK” drives preferential, common light chain efficient pairing of different antibody chains to (cLC) antibody panels create multispecific functionality

Our Science — Multiclonics® Technology Leading the Next Generation of Multispecific Antibody Therapies Common Light Chain (cLC) Antibodies Multiclonics® Format to prevent heavy/light chain mispairing without the need for engineering Target 2 cancer cell Biclonics® Target 1 common light chain immune cell common IgG format cancer light chain cell Triclonics™ DEKK dimerization immune cell technology 21Our Science — Multiclonics® Technology Leading the Next Generation of Multispecific Antibody Therapies Common Light Chain (cLC) Antibodies Multiclonics® Format to prevent heavy/light chain mispairing without the need for engineering Target 2 cancer cell Biclonics® Target 1 common light chain immune cell common IgG format cancer light chain cell Triclonics™ DEKK dimerization immune cell technology 21

Our Research — Triclonics™ and Beyond Triclonics™ Opportunity TARGET 3 common light chain • High throughput production, purification and screening in the trispecific format TARGET 1 TARGET 2 • Stable format with predictable behavior that can be produced as if it were a normal monoclonal antibody common common • Allows for 3 specificities without the need to engineer each light chain light chain individual Fab IgG DEKK • Leverages Merus’ extensive library of established antibody format dimerization panels that bind tumor antigens and engage and modulate the technology immune system to explore combinations and novel biology Triclonics™ 22Our Research — Triclonics™ and Beyond Triclonics™ Opportunity TARGET 3 common light chain • High throughput production, purification and screening in the trispecific format TARGET 1 TARGET 2 • Stable format with predictable behavior that can be produced as if it were a normal monoclonal antibody common common • Allows for 3 specificities without the need to engineer each light chain light chain individual Fab IgG DEKK • Leverages Merus’ extensive library of established antibody format dimerization panels that bind tumor antigens and engage and modulate the technology immune system to explore combinations and novel biology Triclonics™ 22

Merus Overview Oncology-focused Company Developing Multispecific Antibody Therapies Bispecific and trispecific cancer therapeutic candidates based on the human IgG format Established Clinical Pipeline Clinical proof-of-concept with zenocutuzumab (“Zeno”) in patients with neuregulin 1 (NRG1) positive gene fusion (NRG1+) cancers Near Term Data Readouts and Strong Cash Position into 2H 2022 Zeno NRG-1 phase 1/2 clinical data 2Q 2021 Leading Multispecific Antibody (Multiclonics®) Platforms Common light chain format permits broad high throughput Biclonics® and Triclonics™ discovery Strategic Collaborations to Unlock Platform Value Multiple strategic collaborations and license agreements 23Merus Overview Oncology-focused Company Developing Multispecific Antibody Therapies Bispecific and trispecific cancer therapeutic candidates based on the human IgG format Established Clinical Pipeline Clinical proof-of-concept with zenocutuzumab (“Zeno”) in patients with neuregulin 1 (NRG1) positive gene fusion (NRG1+) cancers Near Term Data Readouts and Strong Cash Position into 2H 2022 Zeno NRG-1 phase 1/2 clinical data 2Q 2021 Leading Multispecific Antibody (Multiclonics®) Platforms Common light chain format permits broad high throughput Biclonics® and Triclonics™ discovery Strategic Collaborations to Unlock Platform Value Multiple strategic collaborations and license agreements 23