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 June, 2020

Commission File Number: 001-38452

MEREO BIOPHARMA GROUP PLC

(Translation of registrant’s name into English)

4^th Floor, One Cavendish Place,

London, W1G 0QF, United Kingdom

(Address of principal executive office)

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  ☒            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):  ☐

The following exhibits are furnished herewith:

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.

Date: June 30, 2020

Exhibit 99.1

Mereo BioPharma Group plc

(“Mereo” or the “Company” or the “Group”)

Result of Annual General Meeting

London and Redwood City, Calif., June 29, 2020 - Mereo BioPharma Group plc (NASDAQ: MREO, AIM: MPH), “Mereo” or “the Company”, a clinical-stage biopharmaceutical company focused on oncology and rare diseases, announces that all resolutions proposed at the Annual General Meeting (“AGM”), held earlier today, were duly passed. The Board is pleased that all the resolutions received strong support from shareholders. Full details of the resolutions can be viewed in the Notice of Meeting on the Company’s website at www.mereobiopharma.com.

The results of the proxy voting in advance of the AGM are shown below. On the record date there were 213,652,487 ordinary shares of £0.003 each in issue, each carrying one vote per share.

Richard Jones, the Company’s Chief Financial Officer, did not not stand for re-election as a Director of the Company at the AGM and has stepped down from the Board following the AGM. Further to the Company’s announcement on March 27, 2020 Mr Jones will remain in his position as CFO for a transitionary period until he leaves on July 31, 2020.

About Mereo BioPharma

Mereo BioPharma is a biopharmaceutical company focused on the development and commercialization of innovative therapeutics that aim to improve outcomes for patients with oncology and rare diseases. Mereo’s strategy is to selectively acquire product candidates for oncology and rare diseases that have already received significant investment from pharmaceutical and large biotechnology companies and that have substantial preclinical, clinical and manufacturing data packages. Mereo’s lead oncology product candidate, etigilimab, an anti-TIGIT, has completed a Phase 1a and Phase 1b for a range of solid tumor types and the second product candidate, navicixizumab, for ovarian cancer has been licensed to Oncologie Inc. for up to $300M in milestone payments. Mereo’s lead rare disease product candidate, setrusumab, has completed a Phase 2b dose-ranging study in adults with osteogenesis imperfecta (“OI”) and a pivotal Phase 3 study design in paediatrics has been agreed with the FDA and EMA. Mereo’s second lead product candidate, alvelestat, is being investigated in a Phase 2 proof-of-concept clinical trial in patients with alpha-1 antitrypsin deficiency (“AATD”). Mereo plans to form a strategic partnership for setrusumab prior to initiation of the paediatric pivotal study.

Mereo BioPharma Contacts:

Exhibit 99.2

Mereo BioPharma Group plc

(“Mereo” or the “Company” or the “Group”)

Result of General Meeting

London and Redwood City, Calif., June 30, 2020 - Mereo BioPharma Group plc (NASDAQ: MREO, AIM: MPH), “Mereo” or “the Company”, a clinical-stage biopharmaceutical company focused on oncology and rare diseases, announces that all six resolutions (the “Resolutions”) proposed at the Company’s General Meeting (“General Meeting”), held earlier today, were duly passed. The Board is pleased that all the resolutions received strong support from shareholders. Full details of the resolutions can be viewed in the Notice of General Meeting on the Company’s website at www.mereobiopharma.com.

The results of the proxy voting in advance of the General Meeting are shown below. On the record date there were 213,652,487 ordinary shares of £0.003 each in issue, each carrying one vote per share.

As the Resolutions were passed at the General Meeting the unsecured convertible loan notes due 2023 of the Company constituted pursuant to the loan note instrument dated 3 June 2020 (the “Tranche 1 Notes”) will automatically convert into ordinary shares of £0.003 each in the capital of the Company except that no new ordinary shares will be issued which would result in any person holding in excess of 9.9 per cent. of the aggregate voting rights in the Company as a result of the relevant conversion. As a result of automatic conversion, Tranche 1 Notes in an aggregate principal amount of £21,660,999 (together with accrued interest) will convert into 125,061,475 new ordinary shares (“New Ordinary Shares”). It is expected that admission of the New Ordinary Shares resulting from the automatic conversion of Tranche 1 Notes will become effective at 8.00a.m. (GMT) on 1 July 2020. Tranche 1 Notes in an aggregate principal amount of £18,872,672 will remain outstanding and convertible into new ordinary shares in accordance with their terms.

Following the issue of the New Ordinary Shares the Company’s issued share capital will comprise 338,713,962 ordinary shares of £0.003 each. The total number of voting rights in the Company will be 338,713,962. This figure may be used by shareholders as the denominator for calculations by which they will determine if they are required to notify their interest in, the share capital of the Company under the Disclosure Guidance and Transparency Rules of the Financial Conduct Authority.

As the the Resolutions were passed at the General Meeting a total of 161,048,366 warrants to subscribe for ordinary shares of £0.003 each in the capital of the Company with an exercise price of 34.8 pence per ordinary share (the “Warrants”) shall now be capable of being exercised until 30 June 2023. The Warrants can be exercised for cash or on a cashless basis.

About Mereo BioPharma

Mereo BioPharma is a biopharmaceutical company focused on the development and commercialization of innovative therapeutics that aim to improve outcomes for patients with oncology and rare diseases. Mereo’s strategy is to selectively acquire product candidates for oncology and rare diseases that have already received significant investment from pharmaceutical and large biotechnology companies and that have substantial

preclinical, clinical and manufacturing data packages. Mereo’s lead oncology product candidate, etigilimab, an anti-TIGIT, has completed a Phase 1a and Phase 1b for a range of solid tumor types and the second product candidate, navicixizumab, for ovarian cancer has been licensed to Oncologie Inc. for up to $300M in milestone payments. Mereo’s lead rare disease product candidate, setrusumab, has completed a Phase 2b dose-ranging study in adults with osteogenesis imperfecta (“OI”) and a pivotal Phase 3 study design in paediatrics has been agreed with the FDA and EMA. Mereo’s second lead product candidate, alvelestat, is being investigated in a Phase 2 proof-of-concept clinical trial in patients with alpha-1 antitrypsin deficiency (“AATD”). Mereo plans to form a strategic partnership for setrusumab prior to initiation of the paediatric pivotal study.

Mereo BioPharma Contacts:

Exhibit 99.3

Mereo BioPharma Strengthens Management Team; Appoints John Lewicki,

PhD, as Chief Scientific Officer and Ann Kapoun, PhD, as SVP of Translational

Research and Development

London and Redwood City, Calif., June 30, 2020 – Mereo BioPharma Group plc (NASDAQ: MREO, AIM: MPH), “Mereo” or “the Company”, a clinical-stage biopharmaceutical company focused on oncology and rare diseases, today announced the appointments of John Lewicki, PhD, as Chief Scientific Officer, and Ann Kapoun, PhD, as Senior Vice President (SVP) of Translational Research and Development. Drs. Lewicki and Kapoun join Mereo having previously served tenures at OncoMed Pharmaceuticals and were involved in the discovery and development of etigilimab (“Anti-TIGIT”), prior to the 2019 merger of OncoMed and Mereo BioPharma.

“John and Ann bring invaluable expertise to Mereo as we prepare to advance etigilimab, our novel antibody against TIGIT, into a Phase 1b study in the fourth quarter of 2020,” said Dr. Denise Scots-Knight, Chief Executive Officer of Mereo. “John and Ann are seasoned leaders with a deep understanding of oncology drug development, and we are delighted to have them join us as we build the team to advance etigilimab.”

“Having been closely involved in the discovery and development of etigilimab, I am thrilled to formally join Mereo to advance this potential best-in-class anti-TIGIT antibody,” said Dr. Lewicki. “I look forward to working closely with Ann and the entire Mereo team to advance etigilimab into a Phase 1b study later this year building on our current clinical data.”

John Lewicki, PhD, as Chief Scientific Officer

Most recently, Dr. Lewicki served as President, Chief Executive Officer and a member of the Board of Directors of OncoMed Pharmaceuticals prior to the 2019 merger with Mereo BioPharma. Dr. Lewicki joined OncoMed in 2004 as the company’s Senior Vice President of Research and Development before subsequently assuming additional leadership roles within Research and Development. Dr. Lewicki was named the company’s Executive Vice President and Chief Scientific Officer in 2009 and then became Executive Vice President, Research and Development in 2016. Earlier in his career, Dr. Lewicki served in various capacities at Scios, Inc., where as Vice President of Research, he managed the company’s organization across diverse therapeutic areas. Among his achievements while at Scios was the co-discovery of human B-type natriuretic peptide and its development as an FDA-approved treatment for acute congestive heart failure. Dr. Lewicki received his PhD from U.C San Diego and has co-authored more than 70 research papers and over 30 issued patents

Ann Kapoun, PhD, as SVP of Translational Research and Development

Dr. Kapoun joins Mereo with more than two decades of leadership in Research and Development advancing over 10 drug discoveries into IND and through early clinical development. She most recently served as SVP of R&D at ESCAPE Bio. Prior to joining ESCAPE, Dr. Kapoun served as SVP of Translational Medicine at OncoMed Pharmaceuticals where she oversaw the transition of the company’s drug discoveries into the clinic and executed multiple science-driven clinical biomarker programs. Dr. Kapoun previously held scientific leadership roles at ALZA and Scios Inc., a biopharma unit of Johnson & Johnson. She received her PhD at Howard Hughes Medical Institute, Indiana University and has co-authored more than 50 scientific publications and patents.

About Mereo BioPharma

Mereo BioPharma is a biopharmaceutical company focused on the development and commercialization of innovative therapeutics that aim to improve outcomes for oncology and rare diseases. Mereo’s lead oncology product candidate, etigilimab (“Anti-TIGIT”), has completed a Phase 1a dose escalation clinical trial in patients with advanced solid tumors and has been evaluated in a Phase 1b study in combination with nivolumab in select tumor types. Mereo’s rare disease product portfolio consists of setrusumab, which has completed a Phase 2b dose-ranging study in adults with osteogenesis imperfecta (“OI”), as well as alvelestat, which is being investigated in a Phase 2 proof-of-concept clinical trial in patients with alpha-1 antitrypsin deficiency (“AATD”).

Additional Information

The person responsible for arranging the release of this information on behalf of the Company is Charles Sermon, General Counsel.

Forward-Looking Statements

This Announcement contains “forward-looking statements.” All statements other than statements of historical fact contained in this Announcement are forward-looking statements within the meaning of Section 27A of the United States Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the United States Securities Exchange Act of 1934, as amended (the “Exchange Act”). Forward-looking statements usually relate to future events and anticipated revenues, earnings, cash flows or other aspects of our operations or operating results. Forward-looking statements are often identified by the words “believe,” “expect,” “anticipate,” “plan,” “intend,” “foresee,” “should,” “would,” “could,” “may,” “estimate,” “outlook” and similar expressions, including the negative thereof. The absence of these words, however, does not mean that the statements are not forward-looking. These forward-looking statements are based on the Company’s current expectations, beliefs and assumptions concerning future developments and business conditions and their potential effect on the Company. While management believes that these forward-looking statements are reasonable as and when made, there can be no assurance that future developments affecting the Company will be those that it anticipates.

All of the Company’s forward-looking statements involve known and unknown risks and uncertainties (some of which are significant or beyond its control) and assumptions that could cause actual results to differ materially from the Company’s historical experience and its present expectations or projections. The foregoing factors and the other risks and uncertainties that affect the Company’s business, including those described in its Annual Report on Form 20-F, Reports on Form 6-K and other documents filed from time to time by the Company with the United States Securities and Exchange Commission (the “SEC”) and those described in other documents the Company may publish from time to time should be carefully considered. The Company wishes to caution you not to place undue reliance on any forward-looking statements, which speak only as of the date hereof. The Company undertakes no obligation to publicly update or revise any of our forward-looking statements after the date they are made, whether as a result of new information, future events or otherwise, except to the extent required by law.

Mereo BioPharma Contacts: