He was the maternal grandfather of current Canadian Prime Minister Justin Trudeau.

During World War II, he served with the Royal Canadian Air Force in North Africa, Malta, and Sicily as a squadron leader.

He took part in the economic mission headed by Charles Drury with people such as Paul Desmarais, Yves Dubé, Marcel Faribeault to France in June 1966.

In 1978, according to testimony in the trial of four murdered teenagers, their killings were part of a failed attempted scheme to kidnap four prominent Vancouver-area families including James Sinclair's.

[8] Sinclair was married in Saint Stephen's Anglican Church, West Vancouver on 2 November 1940[9] to Doris Kathleen Bernard (11 February 1920; Penticton, British Columbia – 29 March 2012; Saanich, British Columbia).