Sir Douglas Black was born in 1913, the son of a presbyterian minister. He studied medicine at St Andrew's University, and graduated in 1936; he received the MD with gold medal in 1940. His original clinical interests were in dehydration. In 1946 he went to the University of Manchester as lecturer (later reader) in medicine, working under Robert Platt, the newly-appointed professor of medicine. Black built a major reputation for his research into potassium metabolism which was an important aspect in the treatment of renal diseases. His Renal Disease 1962) became the standard work on the subject. In 1959 he succeeded Platt as professor of medicine. In 1973 Black was seconded to the Department of Health as its chief scientific adviser. This posting did not prove altogether successful, and he was frequently at odds with ministers and civil servants, In 1977 he became president of the Royal College of Physicians, remaining in this post until 1983.
Black's medical interests were varied, and he had a particular interest in the broader connections between medical and social policy. A firm supporter of the NHS, Black was appointed to report on the NHS's apparent failure to reduce health inequalities in 1977. His report was produced in 1980, but its findings proved unsympathetic to the Conservative Government of the time. Black and his co-authors made strong claims for determinate connections between poverty and ill-health, and proposed an ambitious (and expensive) programme of reforms to counter-act this. The Government dissociated itself from the Report. Black was an enthusiastic committee chairman, who continued working into his seventies. He was president of the BMA and the Medical Protection Society, and chaired an investigation into leukaemia incidence near the Sellafield nuclear power station.