Robert Platt was a medical graduate of Sheffield university. He spent his early professional career in Sheffield where he was a demonstrator in pathology at the University and a clinical pathologist at the Royal Infirmary. From 1931-1945 he was a physician at the Sheffield Royal Infirmary. During the Second World War, he served in the RAMC. In 1945 he was elected to the chair of medicine (full-time) at the University of Manchester. Platt was a specialist in kidney disease, undertaking important work on the functional pathology of renal failure. He also undertook research into hypertension. In 1934 he published Nephritis and allied diseases. At Manchester Platt built up a successful research team in renal medicine.
Platt held a number of public appointments. He was chairman of the Joint Working party on the Medical Staffing Structure in the Hospital Service, and chaired a committee of the Royal College of Physicians which investigated the links between smoking and cancer.In 1957 he was elected president of the RCP, and held this post until 1962. Platt was also president of Manchester Medical Society in 1962-3. Platt was appointed baronet in 1959, and was made a life peer in 1967 as Baron Platt of Grindleford; he sat as a cross-bencher and made many contributions to medical debates. His autobiography Private and controversial was published in 1972 a keen cellist, Platt was chairman of the Manchester Chamber Concerts Society from 1952-65. Platt's wife, Margaret Irene Platt, née Cannon, b 1900 (MB ChB Sheff 1922) was a psychiatrist in Manchester and from 1941 to 1946 was in general practice.