He played as an outside right. As a youngster, he was on the books of Heart of Midlothian, but never played in competitive first-team football for the club He went on to play for junior club Musselburgh Athletic before joining First Division club Falkirk in January 1938.
He made what the Scotsman described as "quite a promising debut" in the Scottish Cup defeat of Street Mirren on 12 February, and in the absence of several regular players through injury, made his Scottish First Division debut the following week, in a 2–0 home defeat to Motherwell.
At the end of the 1938-1939 season, Falkirk intended to retain Sinclair, but they accepted a £475 offer for his services from English Second Division club Chesterfield, and Sinclair became one of twelve new arrivals ahead of the 1939-1940 season. He remained with Darlington for two seasons, scoring 11 goals from 68 League appearances.
Sinclair died in Darlington in 1993 at the age of 78.