Sheila Sim was born in Liverpool on 5th June 1922 to banker Stuart Grant Sim and his wife Ida Isabel (née Carter) . The family was living in her grandfather's house at 26 Garth Drive L18 in Allerton but moved whilst she was young to Purley. After attending Croydon High School she first ventured into banking as a career but not taking to the routine of the job she bagan a two year period of study at RADA. It was there that she met her future husband, another budding actor aiming for stardom, Richard Attenborough. The couple were married after he left the RAF and for a while their careers ran in tandem. After a variety of stage roles she made her first film appearance in Powell and Pressburger's 1944 film A Canterbury Tale and in 1948 was cast in The Guinea PIg in which her husband had the leading role.
Sim and Attenborough also worked together in Dancing With Crime (1947) and The Magic Box (1951). In 1952 the couple appeared together in the first night ofthe record breaking The Mousetrap, taking a 10% profit share which served them well until Richard Attenborough was forced to sell it to support his epic film Gandhi.
She had always intended to put family before career and after the arrival of their three children she left the acting profession, her final film appearance being in 1955. The Attenboroughs lived for many years at Richmond and eventually moved into Denville Hall, a residential home for retired actors in North London where they had rooms adjacent to her brother Gerald Sim.
She died on 5th June 1922 aged 93.
