Serge Lajeunesse was a useful role player in parts of five NHL seasons. During the early stages of his career he played defence but later found a home on right-wing where he was a decent goal scorer.
The Montreal native played Junior B with the hometown Beavers in 1967-68. This was followed by two solid years with the Montreal Junior Canadiens where he was selected to the OHA second all-star team both years. In 1970, he was selected in the first round, 12th overall, by the Detroit Red Wings at the Amateur Draft. The youngster played 62 games as a rookie with a weak Wings squad in 1970-71. Over the next two years he was part time player for the club but was reliable performer in the AHL and CHL.
In May 1973, Lajeunesse was traded to the Philadelphia Flyers but dressed for only six games with them. Most of his hockey was played with AHL's Richmond Robins where he displayed offensive prowess as a right-winger until retiring in 1976.