Over fifteen seasons, he played for the Toronto Maple Leafs, Detroit Red Wings, New York Rangers, and Los Angeles Kings.

Stemkowski is best remembered for his heroics in the 1970–71 Stanley Cup semifinals when he scored two overtime goals for the New York Rangers in an eventual series loss to the Chicago Black Hawks.

Considered a textbook "two-way" centre, able to kill penalties and play defence as well as scoring goals, Stemkowski is also remembered as one of the top faceoff takers of the NHL.

But the focus fell upon aging veterans like Terry Sawchuk, Johnny Bower, George Armstrong, Allan Stanley, Frank Mahovlich and Tim Horton.

He was part of a six-player blockbuster transaction in which he was traded along with Frank Mahovlich and Garry Unger from the Maple Leafs to the Red Wings for Norm Ullman, Paul Henderson and Floyd Smith on March 4, 1968.

The Maple Leafs and Red Wings were in fifth and sixth place respectively at the bottom of the East Division standings at the time of the deal.

A good mix of veterans like Rod Gilbert, Jean Ratelle and Ed Giacomin with enthusiastic help from young players such as Stemkowski, Brad Park, Steve Vickers and Walt Tkaczuk.

Despite the Rangers losing a 1971 Stanley Cup semifinal series in seven games to the Chicago Black Hawks, Stemkowski scored game-winning overtime goals in each of two matches.

He has served a stint as the television (1992–1996) and radio colour commentator (2000–2005) for the San Jose Sharks and now does so for the New York Rangers on a part-time basis.

On May 7, 1982, Stemkowski pleaded guilty to a single misdemeanor count of criminal solicitation in Nassau County, New York.

He offered $20,000 to an undercover Nassau County police officer to fly to California and break an ankle and wrist of the business associate.