Sinclair married Ann Briscoe in 1962 and they had three children: Belinda, Crispin and Bartholomew. The marriage was dissolved in 1985.
 In 2010 he married Angie Bowness, whom he divorced in 2017.
Sinclair is a poker player and appeared in the first three seasons of the
Late Night Poker television series in Britain. He won the first season final of the
Celebrity Poker Club
spin-off. On his religious views, Sinclair calls himself an atheist.
 He is a member of British
Mensa and was chairman for 17 years from 1980 to 1997.
 Sinclair was awarded an Honorary Degree (Doctor of Science) by the
University of Bath in 1983.
Despite his involvement in computing, Sinclair does not use the
Internet, stating that he does not like to have "technical or mechanical things around me" as it distracts from the process of invention.
 In 2010 he stated that he does not use computers himself, and prefers using the telephone rather than