He spent his entire twelve-year National Hockey League (NHL) playing career with the Montreal Canadiens (1967–1979) and was a part of eight Stanley Cup championship teams in 1968, 1969, 1971, 1973, 1976, 1977, 1978 and 1979.

He currently works as a special assignment coach for the New York Islanders, a position he previously held with the Toronto Maple Leafs.

Lemaire learned to execute his slapshot when he was young using a heavy steel puck, making his shot second only to that of Bobby Hull for speed and accuracy.

[6] In his bestselling book The Game former Montreal goalie Ken Dryden described a magical relationship on ice that was developing between Lemaire and Guy Lafleur, who complemented each other's speed and shooting ability.

Lemaire's NHL playing career ended following the 1978–79 season when he surprisingly rejected the Canadiens' contract extension offer of $225,000 for each of five years.

Lemaire was head coach of the Canadiens from 1983–1985 and the New Jersey Devils from 1993 to 1998, winning the Stanley Cup in 1995 for the 11th time, and the Jack Adams Award in 1994 and 2003.

Lemaire is known for his unorthodox coaching style for several reasons: first, he prefers a defensive-minded system, often using a strategy called the neutral zone trap.

An example was provided by Terry Frei of ESPN.com in an article posted on August 4, 2008: He [Lemaire] helped drag down the entertainment quotient in this league, and despite all the talk about the Wild being a skating team that uses speed and pounces on turnovers, not all the elements of the trap have disappeared from Minnesota's game.

He joined Lindy Ruff and Ken Hitchcock as assistants to head coach Mike Babcock and helped Team Canada to the gold medal.