6-K

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 October 2025

Commission File Number: 001-38097

ARGENX SE

(Translation of registrant’s name into English)

Laarderhoogtweg 251101 EB Amsterdam, 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 October 3, 2025, 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 Reporton Form 6-K, including Exhibit 99.1, shall be deemed to be incorporated by reference into the Company’s Registration Statementson Forms S-8 (File Nos. 333-225375, 333-258253, and 333-274721), and to be part thereof from the date on which this CurrentReport on Form 6-K is filed, to the extent not superseded by documents or reports subsequently filed or furnished.

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****announces Extraordinary General Meeting of Shareholders on November 18, 2025

October3, 2025

Amsterdam,the Netherlands – argenx SE (Euronext & Nasdaq: ARGX), a global immunology company committed to improving the lives of people suffering from severe autoimmune diseases, today announced that the Extraordinary General Meeting of shareholders will be held at 14:00 CET on Tuesday, November 18, 2025 at the offices of Freshfields LLP (Netherlands), Strawinskylaan 10, 1077 XZ Amsterdam, the Netherlands.

The shareholders and all other persons with meeting rights are invited to attend the Extraordinary General Meeting of shareholders. The formal notice of convocation (including information on attending the meeting in person or by proxy, requirements for notification and registration for the meeting and regarding the e-voting system) is available on the argenx website www.argenx.com and on www.abnamro.com/evoting.

Agenda

argenx has proposed the adoption of a revised remuneration policy during the meeting. The agenda for the meeting as well as all ancillary documents relevant for the meeting are available via the argenx website and are also available for inspection at the argenx offices. A free copy thereof may also be obtained by e-mailing legal@argenx.com. argenx would like to encourage shareholders to use the voting by (electronic) proxy option as referred to in the convocation.

About argenx

argenx is a global immunology company committed to improving the lives of people suffering from severe autoimmune diseases. Partnering with leading academic researchers through its Immunology Innovation Program (IIP), argenx aims to translate immunology breakthroughs into a world-class portfolio of novel antibody-based medicines. argenx developed and is commercializing the first approved neonatal Fc receptor (FcRn) blocker and is evaluating its broad potential in multiple serious autoimmune diseases while advancing several earlier stage experimental medicines within its therapeutic franchises. For more information, visit www.argenx.com and follow us on LinkedIn, Instagram, Facebook, and YouTube.

For further information, please contact:

Media:

Ben Petok

BPetok@argenx.com

Investors:

Alexandra Roy

aroy@argenx.com