He has been Professor Emeritus, University of London, since 1990. An immunologist, he is the co-discoverer with Peter Medawar and Rupert Billingham of acquired immunological tolerance. They injected cells from donor mice into fetal mice, and later neonatal mice, which would as adults receive donor skin grafts without rejection.
To avoid persecution in the largely non-Jewish Köslin, his family placed him in the Jewish Orphanage Berlin-Pankow in Berlin in 1936. In 1938, at age 13, to escape the rising anti-Semitism of the Sturmabteilung (Storm Troopers) and teachers, Brent was sent to England on the first of the Kindertransports and became a pupil at Anna Essinger's Bunce Court School. His parents and older sister stayed behind in Germany. Because his status as a German national would have made him liable to execution in the event of capture, he was advised to change his name. After the war, he found out that his parents were sent to Riga, Latvia and executed. There are three stolpersteine for his parents and sister in Berlin. After the war, he became a British citizen and enrolled at University of Birmingham.
- Laboratory technician, 1941–43
- Army service, 1943–47, Captain
- Lecturer, Department of Zoology, UCL, 1954–62
- Rockefeller Research Fellow, California Institute of Technology, 1956–57
- Research scientist, National Institute for Medical Research, 1962–65
- Professor of Zoology, University of Southampton, 1965–69
- Professor of Immunology, St. Mary's Hospital Medical School, London, 1969–90
- European Editor, Transplantation, 1963–68
- Chairman: Wessex Branch, Institute of Biology, 1966–68
- General Secretary, British Transplantation Society, 1971–75
- President, The Transplantation Society, 1976–78
- Leslie Baruch Brent, Sunday's child? A Memoir. Bank House Books, 2009, ISBN 978-1-904408-44-4
- Anthea Gerrie, "Revealed: the wartime school that saved lives" The Jewish Chronicle (August 11, 2011). Retrieved September 29, 2011
- Howard Spier, "Leslie Baruch Brent: Ein Sonntagskind" (PDF) AJR Journal (November 2004), p. 11. Retrieved October 4, 2011
- Leslie Baruch Brent, "Building Bridges to Berlin" (PDF) AJR Journal (August 2008), p. 15. Retrieved October 12, 2011
- Brent, Leslie (15 July 2014). "To ask for support for the Israeli soldiers who are engaged in such death and destruction is an abomination". jfjfp.com. Retrieved 18 July 2014.