Sweetnam was born on 5 February 1927, in Wimbledon, south London, to Irene (née Black), a former medical student, and William Sweetnam, a GP.

[1] From 1950 to 1952 he undertook National Service as a surgeon-lieutenant aboard HMS Vanguard.

[2] He was also a consultant adviser in orthopaedic surgery to the United Kingdom's Department of Health from 1981 to 1990.

[1][3] He was also president of the British Orthopaedic Association (1985); and a Fellow of University College London.

[2] He was made a Commander of the Order of the British Empire (CBE) in the 1990 New Year Honours[4] and a Knight Commander of the Royal Victorian Order (KCVO) in the 1992 New Year Honours.