Sergei Kostitsyn was born March 20, 1987 in Novopolotsk, Belarus. The seventh round, 200th overall selection of the Montreal Canadiens in the 2005 NHL Entry Draft, Kostitsyn is a graduate of the OHL's London Knights. He is the brother of Andrei Kostsitsyn.
A solid two way player with excellent offensive capabilities, Kostsitsyn spent two seasons honing his skills with the London Knights before he made the leap to the pro ranks. His most productive season with the Knights came in 2006-07 when the Belarusian tallied a whopping 131 points in 59 games.
Kostitsyn made his professional hockey debut with the Hamilton Bulldogs at the start of the 2007-08 regular season. After leading the Bulldogs in scoring, the winger was called up by the Montreal Canadiens. Kostitsyn would appear in 52 games throughout that season and finish 14th among NHL rookie goal scoring.
After splitting three seasons between Montreal and Hamilton, the younger of the Kostitsyn brothers was traded to the Nashville Predators on June 29, 2010, in exchange for forward Dustin Boyd and goaltender Dan Ellis.