UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the Month of May 2020

Commission File Number: 001-38097

ARGENX SE

(Translation of registrant’s name into English)

Willemstraat 5
4811 AH, Breda, the Netherlands

(Address of principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F  x     Form 40-F  ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1): ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): ¨

EXPLANATORY NOTE

On May 14, 2020, argenx SE (the “Company”) issued a press release, a copy of which is attached hereto as Exhibit 99.1 and is incorporated by reference herein.

The information contained in this Current Report on Form 6-K, including Exhibit 99.1, is incorporated by reference into the Company’s Registration Statements on Forms F-3 (File No. 333-225370) and S-8 (File No. 333-225375).

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Exhibit 99.1

argenx reports first quarter 2020 financial results and provides business update

- Topline data readout from Phase 3 ADAPT trial of efgartigimod in generalized myasthenia gravis on track for mid-2020 and Biologics License Application filing by end of year -

- Enrollment paused in ongoing trials under Janssen and LEO Pharma collaborations -

- ARGX-117 being evaluated in COVID-19 patients with acute respiratory distress syndrome in collaboration with UZ Gent –

- Management to host conference call today at 3:00 pm CEST (9:00 am ET) -

May 14, 2020

Breda, the Netherlands / Ghent, Belgium – argenx (Euronext & Nasdaq: ARGX), a clinical-stage biotechnology company developing a deep pipeline of differentiated antibody-based therapies for the treatment of severe autoimmune diseases and cancer, today announced its financial results for the first quarter ended March 31, 2020 and provided a business update.

“We are very excited to be approaching our first pivotal Phase 3 data readout with topline data from the ADAPT trial still on track for mid-year. This is an important milestone as it will precipitate our transition from a late-stage development company towards an integrated commercial organization. We have been investing in the expansion of our commercial infrastructure and are preparing for a 2021 launch of efgartigimod in gMG in the U.S., if approved,” stated Tim Van Hauwermeiren, CEO of argenx.

“Over the last several months, the COVID-19 global pandemic has presented an unprecedented challenge, and as we face uncertainty in the coming months, we are grateful to have strong fundamentals across our business and the ability to fund our deep antibody pipeline. I am most grateful, however, for the continued support of our employees who have demonstrated exceptional focus and an unwavering dedication to our mission of developing therapies for the treatment of severe autoimmune diseases and cancer. This commitment is underscored by our decision to evaluate the potential of ARGX-117 to attenuate complement activation in severe respiratory illness associated with COVID-19 while obtaining key metrics of our drug candidate in this first-in-human trial.”

FIRST QUARTER 2020 AND RECENT HIGHLIGHTS

argenx commitment to its people, patients and business

Despite the challenges of the COVID-19 pandemic, argenx remains focused on executing on its “argenx 2021” vision to become a fully integrated, global immunology company. In order to minimize impact on employees, patients and their communities, physicians and ongoing business priorities, argenx has implemented measures across its organization and in the operation of its globally run clinical trials.

Efgartigimod trials remain open with additional registrational trials expected to launch this year

Efgartigimod is currently being evaluated in four targeted indications where IgG autoantibodies are directly pathogenic. A fifth indication is expected to be announced this year.

Janssen and LEO Pharma have paused enrollment of clinical trials of cusatuzumab and LP0145 (ARGX-112)

Enrollment is paused in two ongoing clinical trials initiated under the global cusatuzumab collaboration and licensing agreement with Cilag GmbH International, an affiliate of the Janssen Pharmaceutical Companies of Johnson & Johnson. Trials that have paused enrollment under the collaboration include:

Additionally, LEO Pharma has paused enrollment of the ongoing trial of LP0145 for the treatment of atopic dermatitis.

Timing to restart enrollment of all trials will depend on the trajectory of COVID-19 infection rates

ARGX-117 being evaluated as potential treatment for ARDS in COVID-19 patients

ARGX-117 is a potentially first-in-class complement-targeting antibody against C2 with potential therapeutic applications in severe autoimmune diseases.

argenx continues to expand its early-stage pipeline

FIRST QUARTER 2020 FINANCIAL RESULTS (CONSOLIDATED)

DETAILS OF THE FINANCIAL RESULTS

Cash, cash equivalents and current financial assets totaled €1,305.5 million on March 31, 2020, compared to €1,335.8 million on December 31, 2019 and €961.6 million on March 31, 2019.

Operating income amounted to €23.4 million for the three months ended March 31, 2020, compared to €40.0 million for the three months ended March 31, 2019. The decrease in the first three months of 2020 was primarily explained by the revenue recognized in the first quarter of 2019, following a $30.0 million development milestone payment received under the AbbVie collaboration agreement.

Research and development expenses increased by €60.1 million during the three months ended March 31, 2020 to reach €94.9 million, compared to €34.8 million for the three months ended March 31, 2019. This planned increase was mainly the result of (i) increased external research and development expenses reflecting higher clinical trial costs and manufacturing expenses related to the development of the argenx product candidate portfolio and (ii) higher personnel expenses as a result of increased costs of the share-based payment compensation plans related to the grant of stock options to argenx research and development employees and increased costs associated with additional research and development employees.

Selling, general and administrative expenses totaled €25.0 million and €11.3 million for the three months ended March 31, 2020 and 2019, respectively. The increase of €13.7 million was principally linked to an increase of personnel expense, resulting from (i) higher costs of the share-based payment compensation plans related to the grant of stock options to its selling, general and administrative employees and (ii) increased costs associated with additional employees recruited to strengthen its selling, general and administrative activities, notably in preparation of the potential commercial launch of efgartigimod in the U.S., if approved.

For the three months ended March 31, 2020, financial income, which primarily relate to interests received on its cash and cash equivalents and current financial assets, amounted to €1.7 million compared to €3.5 million for the same period in 2019. Financial expense amounted to €5.0 million for the three months ended March 31, 2020 and corresponded mainly to a decrease in net asset value on its current financial assets following the impact of the COVID-19 outbreak on the financial markets.

Exchange gains totaled €20.8 million for the three months ended March 31, 2020 compared to €9.5 million for the three months ended March 31, 2019 and were mainly attributable to unrealized exchange rate gains on cash, cash equivalents and current financial assets position in U.S. dollars due to the favorable fluctuation of the EUR/USD exchange rate.

The total comprehensive loss for the three months ended March 31, 2020 was €80.0 million compared to a total comprehensive profit, which was principally due to the milestone payment received from AbbVie as indicated above, of €6.7 million for the three months ended March 31, 2019.

EXPECTED 2020 FINANCIAL CALENDAR:

CONFERENCE CALL DETAILS

The first quarter 2020 results will be discussed during a conference call and webcast presentation today at 3 pm CET/9 am ET. To participate in the conference call, please select your phone number below and use the confirmation code 6736269. The webcast may be accessed on the homepage of the argenx website at www.argenx.com or by clicking here.

Dial-in numbers:

Please dial in 5–10 minutes prior to 3 pm CET/ 9 am ET using the number and conference ID below.

Confirmation Code: 6736269

About argenx

argenx is a global immunology company developing antibody-based medicines for patients suffering from severe autoimmune diseases and cancer. By translating immunology breakthroughs into innovative drug candidates, argenx is building a world-class portfolio of first-in-class antibodies in both early and late clinical-stages of development. argenx is evaluating efgartigimod in multiple serious autoimmune indications and cusatuzumab in hematological malignancies in collaboration with Janssen, along with advancing earlier stage assets within its therapeutic franchises.

www.argenx.com

For further information, please contact:

Beth DelGiacco, Vice President, Investor Relations

+1 518 424 4980

bdelgiacco@argenx.com

Joke Comijn, Director Corporate Communications & Investor Relations (EU)

+32 (0)477 77 29 44

+32 (0)9 310 34 19

jcomijn@argenx.com

Forward-looking Statements

The contents of this announcement include statements that are, or may be deemed to be, “forward-looking statements.” These forward-looking statements can be identified by the use of forward-looking terminology, including the terms “believes,” “estimates,” “anticipates,” “expects,” “intends,” “may,” “will,” or “should” and include statements argenx makes concerning its 2020 business and financial calendar and related plans; the clinical data of its product candidates; the intended results of its strategy and argenx’s, and its collaboration partners’, advancement of, and anticipated clinical development, data readouts and regulatory milestones and plans, including the timing of planned clinical trials and expected data readouts. By their nature, forward-looking statements involve risks and uncertainties and readers are cautioned that any such forward-looking statements are not guarantees of future performance. argenx’s actual results may differ materially from those predicted by the forward-looking statements as a result of various important factors, including argenx’s expectations regarding its the inherent uncertainties associated with competitive developments, preclinical and clinical trial and product development activities and regulatory approval requirements; argenx’s reliance on collaborations with third parties; estimating the commercial potential of argenx’s product candidates; argenx’s ability to obtain and maintain protection of intellectual property for its technologies and drugs; argenx’s limited operating history; and argenx’s ability to obtain additional funding for operations and to complete the development and commercialization of its product candidates. A further list and description of these risks, uncertainties and other risks can be found in argenx’s U.S. Securities and Exchange Commission (SEC) filings and reports, including in argenx’s most recent annual report on Form 20-F filed with the SEC as well as subsequent filings and reports filed by argenx with the SEC. Given these uncertainties, the reader is advised not to place any undue reliance on such forward-looking statements. These forward-looking statements speak only as of the date of publication of this document. argenx undertakes no obligation to publicly update or revise the information in this press release, including any forward-looking statements, except as may be required by law.