Exhibit 5.1

[LETTERHEAD OF SIMPSON THACHER & BARTLETT LLP]

March 25, 2021

Telefonaktiebolaget LM Ericsson

SE-164 83

Stockholm, Sweden

Ladies and Gentlemen:

We have acted as United States counsel to Telefonaktiebolaget LM Ericsson, a Swedish limited liability company (the “Company”), in connection with the Registration Statement on Form F-3 (the “Registration Statement”) filed by the Company with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended, relating to the issuance by the Company of debt securities (the “Securities”). The Securities will be issued under an indenture dated as of May 9, 2012 (the “Indenture”) between the Company and Deutsche Bank Trust Company Americas, as trustee (the “Trustee”).

We have examined the Registration Statement and the Indenture, which is an exhibit to the Registration Statement. In addition, we have examined, and have relied as to matters of fact upon, originals, or duplicates or certified or conformed copies, of such records, agreements, documents and other instruments and such certificates or comparable documents of public

Telefonaktiebolaget LM Ericsson March 25, 2021

officials and of officers and representatives of the Company and have made such other investigations as we have deemed relevant and necessary in connection with the opinions hereinafter set forth.

In rendering the opinion set forth below, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as duplicates or certified or conformed copies and the authenticity of the originals of such latter documents. We also have assumed that at the time of execution, authentication, issuance and delivery, as applicable, of the Securities, the Indenture will be the valid and legally binding obligation of the Trustee.

In rendering the opinion set forth below, we have assumed further that (1) the Company is validly existing and in good standing under the law of Sweden and has duly authorized, executed and delivered the Indenture in accordance with its organizational documents and the law of Sweden, (2) the execution, delivery and performance by the Company of the Indenture and the Securities do not constitute a breach or violation of its organizational documents or violate the law of Sweden or any other jurisdiction (except that no such assumption is made with respect to the law of the State of New York) and (3) the execution, delivery and performance by the Company of the Indenture do not constitute a breach or default under any agreement or instrument which is binding upon the Company.

Based upon the foregoing, and subject to the qualifications, assumptions and limitations stated herein, we are of the opinion that assuming (a) the taking of all necessary corporate action by the Board of Directors of the Company, a duly constituted and acting committee of such Board and/or duly authorized officers of the Company (such Board of Directors, committee or

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Telefonaktiebolaget LM Ericsson March 25, 2021

authorized officers being hereinafter referred to as the “Company Authorizing Party”) to approve the issuance and terms of the Securities and the terms of the offering thereof so as not to violate any applicable law or agreement or instrument then binding on the Company and (b) the due execution, authentication, issuance and delivery of the Securities, upon payment therefor in accordance with the applicable definitive underwriting, purchase or similar agreement approved by the Company Authorizing Party and otherwise in accordance with the provisions of such agreement and the Indenture, the Securities will constitute valid and legally binding obligations of the Company enforceable against the Company in accordance with their terms.

Our opinion set forth above is subject to (i) the effects of bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and other similar laws relating to or affecting creditors’ rights generally, (ii) general equitable principles (whether considered in a proceeding in equity or at law), (iii) an implied covenant of good faith and fair dealing and (iv) to the effects of the possible judicial application of foreign laws or foreign governmental or judicial action affecting creditors’ rights. In addition, we express no opinion as to the validity, legally binding effect or enforceability of (A) the waiver of rights and defenses contained in Section 4.4 of the Indenture or (B) Section 10.13 of the Indenture relating to the severability of provisions of the Indenture.

We do not express any opinion herein concerning any law other than the law of the State of New York.

We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement and to the use of our name under the caption “Validity of Securities” in the prospectus included in the Registration Statement.

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Telefonaktiebolaget LM Ericsson March 25, 2021

Very truly yours,

/s/ Simpson Thacher & Bartlett LLP

SIMPSON THACHER & BARTLETT LLPC

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