Mark was born in London in December 1954, the eldest of three children. The family later moved to Hampshire where he attended Portsmouth Grammar School. He won a scholarship at St John’s College, Cambridge in 1973 and went on to undertake a PhD at the Mullard Radio Astronomy Observatory (MRAO) of the Cavendish Laboratory between 1976 and 1979. He completed a thesis on ‘The radio and X-ray properties of clusters of galaxies’, producing nine papers from the work, several with Steve Gull, but all as first author. He subsequently spent two years as a Miller Research Fellow at the University of California, Berkeley, before returning to Cambridge as a Research Fellow of Gonville and Caius College.

It was while back at MRAO that he established his reputation as a world leader in studies of the Cosmic Microwave Background (CMB). He observed for hundreds of hours with the Owens Valley Radio Observatory in California, and in the early 1980s published the first solid detections of the Sunyaev-Zel’dovich (SZ) Effect, the lower CMB temperature observed when CMB photons pass through foreground clusters of galaxies on route to earth. His application of the SZ Effect to determine the scale of the Universe subsequently founded a new and still-thriving field of study.

In 1982 Mark had met fellow British astrophysicist Diana Worrall, then working in California, and they married two years later. Mark crossed the Atlantic again to join the Department of Astronomy at Harvard University, where for part of the time he was also an Alfred P Sloan Foundation Research Fellow. He joined the Smithsonian Astrophysical Observatory in 1992. Mark continued to publish widely, often in collaboration with Diana, on radio, optical and X-ray observations of galaxies and clusters and on the physics of radio jets, also adding theoretical work and papers on gravitational lensing.

Mark was appointed Professor of Cosmology and Astrophysics at the University of Bristol in 1995, becoming head of the Astrophysics Group in the Department of Physics. Combining his research with undergraduate teaching, postgraduate supervision and the administration of the group, particularly the acquisition of research grants, he oversaw the significant increase in size and prestige of the Bristol group and was for a time joint head of the Physics Department. He was also highly respected as a fair and professional reviewer, and greatly in demand to serve on national and international research committees and boards, often as chair. Despite all of this, he and Diana still found time to spend part of their summers back at the Harvard-Smithsonian Center for Astrophysics, working with multiple colleagues in the High Energy Astrophysics and Radio Astronomy divisions.

Mark loved astrophysics! His many pivotal contributions encompass broad and exciting topics including extreme conditions around black holes and the energetic jets they power, the hot gas that permeates rich clusters of galaxies, gravitational lensing, and the role of magnetic fields. He brought his energy, enthusiasm, deep knowledge and clarity of thought to all aspects of his work. His knowledge of radio galaxies was encyclopaedic, with an ability to immediately provide key parameters and properties of any radio source mentioned in passing. He was a gifted mathematician and teacher, in particular teaching the challenging General Relativity course which was popular with students. Mark was an inspiring and exacting collaborator whose input was always insightful and constructive, and a dedicated, inspiring and supportive supervisor and mentor of students. He loved interacting with colleagues and was always generous with his time and ideas. His enthusiasm was infectious, and the significance of his contributions to our field is huge, both scientifically and socially.

Beyond science, Mark also had an unquenchable thirst for knowledge and experiences. He travelled the world and taught himself the language of many of the countries he visited, including China and Sweden where since 2019 he held an affiliated professorship. He was extremely well read, and a bellringer who, with Diana, regularly rang for their local church. In odd, spare moments, he enjoyed a round of golf, demonstrating significant talent with an impressive handicap.

Mark Birkinshaw died of cancer in hospital on 23 July after a brief but serious illness, with his wife and long-time collaborator, Emeritus Professor Diana Worrall, at his side. Mark was a leader in his field, both in the UK and worldwide. He was hugely valued by his colleagues and students in the School of Physics at Bristol and they feel his loss acutely. His early and unexpected death represents a huge loss to both the University and to the worldwide astrophysics community.