Koivu started his professional ice hockey career playing for TPS in the Finnish SM-liiga, in the 1992–1993 season. He spent three seasons with TPS, winning two Finnish championships with the team in 1993 and 1995, and being elected Player of the Year by his fellow players in the 1994–1995 season. He was drafted by the Canadiens in the 1993 NHL Entry Draft as their first-round selection (21st overall), and moved to North America for the 1995-96 season.

 

In his first year, Koivu ranked 4th in scoring amongst NHL rookies. The following season Koivu was the NHL leading scorer (13 goals, 25 assists and 38 points) before suffering a knee injury on December 7, 1996 in a game against Chicago Blackhawks. He missed 22 games in that season but still scoring over a point per game (56 points in 50 games).

 

On September 30, 1999 Koivu was named the 27th captain of the Montreal Canadiens, and the first European-born captain in the history of the Canadiens.

 

After six seasons in the NHL, Koivu was diagnosed with Non-Hodgkin's lymphoma in September 2001 and missed practically the entire 2001-02 NHL season. He made an amazing recovery and was able to return for the playoffs, leading the Canadiens to an unlikely first-round upset of the number one-ranked Boston Bruins. For his courage and off-ice team leadership while undergoing cancer treatment, he was awarded the Bill Masterton Memorial Trophy following the 2002 playoffs. He followed up in the 2002-03 NHL season by scoring his career best single-season point total with 71 (21 goals, 50 assists) to that date.

 

During the 2004-05 NHL lockout, Koivu returned to Finland to play for TPS, whose head coach at the time was his father, Jukka Koivu. He was joined in Turku by then-fellow Montreal Canadien, and close friend, Craig Rivet.

 

The 2006-07 NHL season was Koivu's seventh season as the Canadiens captain. His continued tenure seems to have ended a supposed curse of Habs captains. During a ten-year span from 1989 to 1999, six captains were traded away.

 

The 2006-07 NHL season was for Saku Koivu, personally successful. In a game on January 9, 2007, in which the Montreal Canadiens defeated the Atlanta Thrashers 4-2, he registered his 500th NHL point. With 2:47 remaining, Koivu fed Michael Ryder with a pass across the slot for a power-play goal. Koivu received a standing ovation from the sellout crowd of 21,273 in Montreal. Koivu went on to score 22 goals and 53 assists in 81 games, totaling 75 points, making 2006-07 his best season. At the season's annual awards banquet, Koivu was announced as the winner of the King Clancy Trophy for his role in the cancer-fighting Saku Koivu Foundation. The Canadiens' team doctor, Dr. David Mulder, received the award on Koivu's behalf as he wasn't present.

 

In October 2007, Koivu was criticized by nationalist lawyer Guy Bertrand for not speaking French in a videotaped pre-game ceremony. Although Koivu is fluent in English, Swedish, and Finnish, he speaks limited French and is shy about using it in public. He replied to Bertrand's remarks that he is not perfect, and jokingly mentioned that he speaks French to his wife during intimate moments. Koivu introduced his team in the next pre-game video with the phrase "Ici Saku Koivu, voici mon équipe" ("Saku Koivu here, this is my team").