Theo Dubois was introduced to rowing at the Winnipeg Rowing Club just before his fifteenth birthday. By 1930, Dubois gained a spot on the junior crew and participated in the Northwestern International Rowing Association Regatta, an event which included clubs within a 500-mile radius of Winnipeg. As a junior and senior, Dubois figured prominently in this bi-annual competition and in 1934, he claimed four gold medals in the Singles, Doubles, Fours, and Eights categories. By 1939, Dubois captured the Northwestern Singles Championship on 5 consecutive occasions. That same year Dubois won the Singles title and, with partner Ab Riley, the Senior Doubles at the 57th Royal Canadian Henley Regatta. With the Henley victory, Dubois and Riley were considered the best Senior Doubles pair on the North American continent.
Dubois twice qualified for Olympic competition but was thwarted from participation. In 1940, the outbreak of WWII forced the cancellation of the Games while in 1948, the Olympic Selection Committee decided that Dubois, at the age of 37, would not be a potential point scorer. Interestingly, the winning Singles time at those Olympics was slower than Dubois's time.
In 1978, Dubois was appointed the Honourary President of the Winnipeg Canoe Club after serving as a coach/captain since 1950. Perhaps the most outstanding award Dubois has received during his career was the Lou Marsh Trophy as Canada's Outstanding Athlete of the Year in 1946. From 1931-1955, Dubois acquired more trophies at the Northwestern Regatta than any other oarsman. Dubois did not rest on his laurels and in 1976 and 1977, he captured the Veterans' Singles titles.