Upon qualifying, during
World War II, he joined the
Royal Army Medical Corps in India, While at St Mary's he was heavily influenced by the work of
Donald Winnicott. In 1960 he went to the
University of Sydney as Commonwealth professor of paediatrics. He served as secretary‐general (1965–1974, succeeding
Guido Fanconi) and treasurer (1974–1977) to the
International Paediatric Association, about which he also wrote a history, published in the last year of his life. Reviewing the book in 2008
Rolf Zetterström noted that it was "in some respects [...] more Stapleton's autobiography than a book about IPA" and credited him with "important contributions to paediatrics, such as the elucidation of a near-epidemic of
hyper-calcaemia in infants, due to overdosage of vitamin D." Stapleton held an honorary MD from Sydney, and was a
Fellow of the Royal College of Physicians (FRCP(Lond)), a
Fellow of the Royal Australasian College of Physicians (FRACP) and a
Fellow of the Royal College of Paediatrics and Child Health (FRCPCH). == Retirement and legacy ==