César Milstein was born in Bahía Blanca, Argentina, 8 October 1927, the son of Lázaro and Máxima Milstein. He was educated at the Colegio Nacional, Bahia Blanca, 1939-44, at secondary school in Buenos Aires, and at the University of Buenos Aires, 1945-52. He also worked part-time at the Laboratorios Liebeschutz to fund his studies. He married Celia Prilleltensky in 1953.

He travelled for a year in Europe with his new wife, 1953-4. He studied for a PhD at the Instituto de Quimica Biologica at the University of Buenos Aires, 1954-7, and then joined the staff of the Instituto Nacional de Microbiología, Buenos Aires, 1958. He won a British Council travelling scholarship and chose to study for a PhD in the Department of Biochemistry, Cambridge University, 1958-61. He returned briefly to Argentina as the first head of the Division de Biologia Molecular at the Instituto Nacional de Microbiología, Buenos Aires, 1961-3. Political unrest in Argentina led him to seek a post in Cambridge again and he joined the Medical Research Council (MRC) Laboratory of Molecular Biology, 1963. He remained there until his retirement in 1995, and was successively Head of the Protein Chemistry Subdivision, 1969-80, Joint Head of the Division of Protein and Nucleic Acid Chemistry, 1981-95, and Deputy Director of the Laboratory, 1988-95. His work concentrated on immunology, in particular the structure of antibody proteins and the genetic study of antibody diversification.

He was awarded the Nobel Prize for Medicine jointly with Georges Köhler and Niels Jerne, 1984, for the discovery of monoclonal antibodies. He was elected to the Fellowship of the Royal Society, 1975; created Companion of Honour, 1995; and awarded the Medical Research Council's first Millennium Medal, 2000.

He died in 2002.