Margaret Pickles, known as Peggy, came to the University of Oxford to study botany but switched to physiology, earning her bachelor's degree at Somerville College in Oxford in 1936. After winning a competitive examination she studied for the next three years at the University College Hospital Medical School in London, while completing her medical examinations in Oxford. She qualified as a doctor in 1939 and worked at the Bearsted Maternity Hospital and the Royal East Sussex Hospital in Hastings, returning to Oxford in 1941 to work at the Radcliffe Infirmary as the Nuffield Graduate Assistant in Pathology. She completed her doctorate (D.M.) at Somerville in 1947, which was published as Haemolytic disease of the newborn in 1949 and continued to work as a clinical pathologist and immunologist

In 1950, aged 36, she married Alastair Robb-Smith, a distinguished pathologist who had been appointed Nuffield Reader in Pathology and head of pathology at Oxford's clinical school (now the Nuffield Department of Medicine) in 1937, at the age of 29.

Her interests extended beyond medicine. In 1960 she published (under the name Margaret Pickles) The Birds of Blenheim Park with the Oxford Ornithological Society. She also continued her botanical studies, breeding daffodils at her home, Chaucer's House in Woodstock, Oxfordshire.