Theriault is the longest-serving coach in the history of the Oshawa Generals of the Ontario Hockey League (OHL). He also served as an OHL head coach for both the Erie Otters and Sault Ste. Marie Greyhounds. Theriault was awarded the 1986–87 Matt Leyden Trophy as the OHL Coach of the Year.
At the professional level, Theriault was an assistant coach with the Buffalo Sabres during the 1996–97 NHL season when Ted Nolan won the Jack Adams Award as the NHL's Coach of the Year. He has also served as head coach for the Flint Spirits of the International Hockey League and the HC Asiago of the Italian Serie A.