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 email.