Exhibit 5.1

Dear Sirs, Madams,

1.           We have acted as Dutch law legal advisers to argenx SE (the Company) with respect to certain matters of Netherlands law in connection with, inter alia, (i) the issuance by the Company of (a) 2,333,334 new ordinary shares with a nominal value of EUR 0.10 each in the capital of the Company and (b) up to an additional 350,000 new ordinary shares with a nominal value of EUR 0.10 each in the capital of the Company pursuant to the exercise by the Underwriters of the option to purchase Optional Securities (as defined in the Underwriting Agreement (as defined below)) (New Shares) on the terms and conditions set out in the underwriting agreement (the Underwriting Agreement) entered into between J.P. Morgan Securities LLC, Cowen and Company, LLC and SVB Leerink LLC, as representatives of the Underwriters and the Company on 22 March 2022, of which New Shares under (a): (x) 1,433,701 New Shares are to be delivered in the form of American Depositary Shares, each representing one New Share (ADSs) in a public offering in the United States on The Nasdaq Global Select Market under the United States Securities Act of 1933, as amended (the Securities Act), and the listing of the ADSs on The Nasdaq Global Select Market (the US New Shares) and (y) 899,633 New Shares are to be issued as ordinary shares in a concurrent private placement in the European Economic Area and countries outside the United States and Canada to certain legal entities all of which are qualified investors within the meaning of Regulation 2017/1129 of the European Parliament and of the Council of June 14, 2017 (as amended, the Prospectus Regulation) (the Private Placement) and (ii) the proposed listing of the New Shares on the regulated market of Euronext Brussels (the Transaction). The ordinary shares with nominal value of EUR 0.10 each in the capital of the Company shall hereinafter be defined as the Ordinary Shares.

Freshfields Bruckhaus Deringer LLP is a limited liability partnership registered in England and Wales with registered number OC334789. It is authorised and regulated by the Solicitors Regulation Authority. Dutch Chambers of Commerce registration number 34368197. For regulatory information please refer to www.freshfields.com/support/legalnotice.

A list of the members (and of the non-members who are designated as partners) of Freshfields Bruckhaus Deringer LLP and their qualifications is available for inspection at its registered office, 65 Fleet Street, London EC4Y 1HS or at the above address. Any reference to a partner means a member, or a consultant or employee with equivalent standing and qualifications, of Freshfields Bruckhaus Deringer LLP or any of its affiliated firms or entities. Freshfields Bruckhaus Deringer LLP’s Amsterdam office includes attorneys, civil law notaries, tax advisers and solicitors.

Bank account:
Stg Beh Derdengld Freshfields Bruckhaus Deringer LLP, ABN AMRO Bank N.V., IBAN: NL14ABNA0256049947, BIC: ABNANL2A

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This opinion letter is delivered to you pursuant to your request.

Documents reviewed

The documents referred to above in items (a) to (n) (inclusive) are herein referred to as the Documents; the documents referred to above in items (g) and (k) (inclusive) are herein referred to as the Corporate Documents; and the documents referred to above in item (k) are herein referred to as the Resolutions.

Nature of Opinion and Observations

Opinion

4.           On the basis stated in paragraph 3, and subject to the assumptions in Schedule 1, the qualifications in Schedule 2 and any factual matters, documents or events not disclosed to us, we are of the opinion that when issued pursuant to validly executed Deeds of Issuance and fully paid in US Dollars (and following receipt by the Dutch notary of a bank statement as referred to in Section 2:93a paragraphs 2 and 6 of the Dutch Civil Code) in accordance with the terms of a validly executed Underwriting Agreement and the Articles of Association, each New Share will have been duly authorised, validly issued and fully paid and will be non-assessable.

Benefit of opinion

5.           This opinion is addressed to you in relation to and as an exhibit to the Company’s Current Report on Form 6-K filed in connection with the Transaction (the Current Report) and, except with our prior written consent, is not to be transmitted or disclosed to any other person, other than as an exhibit to the Current Report and is not to be used or relied upon by you or by any other person for any purpose other than in connection with the filing of the Current Report.

6.           This opinion letter and any non-contractual obligations arising out of or in relation to this opinion are governed by the laws of the Netherlands. ¹

7.           We hereby consent to the filing of this legal opinion letter as an exhibit to the Current Report. In giving the consent set out in the previous sentence, we do not thereby admit or imply that we are in the category of persons whose consent is required under Section 7 of the Securities Act or any rules and regulations of the SEC promulgated thereunder.

¹ The general terms and conditions of Freshfields Bruckhaus Deringer LLP can be found at www.freshfields.com.

Yours faithfully,

/s/ Freshfields Bruckhaus Deringer LLP

Freshfields Bruckhaus Deringer LLP

Schedule 1
ASSUMPTIONS

In considering the Documents and in rendering this opinion we have (with your consent and, unless specifically stated otherwise, without any further enquiry) assumed that:

Schedule 2
QUALIFICATIONS

Our opinion is subject to the following qualifications: