Alexander Sinclair played junior hockey with the West Fort William Maroons of the Thunder Bay Hockey League from 1929 through 1931 before spending his first two senior seasons with the Lakehead Woodsmen. He joined the Port Arthur Bearcats in 1933 (when they were known as the Port Arthur Hockey Club) and earned his way to the 1936 Winter Olympics as a member of the Canadian delegation. In six games played he scored three goals as a forward, contributing to Canada’s silver medal at that year’s Olympic tournament. After the Olympics he joined the Wembley Monarchs of the English National League and stayed with them through 1939, at which point he returned to Canada and joined the Fort Frances Maple Leafs for three seasons. He ended his playing career in 1944 after two seasons with the Port Arthur Shipbuilders. Soon after he became manager of the Port Arthur Arena and moved to Cincinnati in 1949 to manage the Cincinnati Gardens. By the 1970s, he was working in Dayton, Ohio at his final job, President and General Manger of the Dayton Arena. As a member of his Olympic team, he was inducted into the Northwestern Ontario Sports Hall of Fame in 1987.