He played for the Atlanta Thrashers, New Jersey Devils, Los Angeles Kings, Montreal Canadiens, and Washington Capitals in the National Hockey League (NHL), as well as Ak Bars Kazan, Khimik Moscow Oblast, SKA Saint Petersburg, Avangard Omsk, and Spartak Moscow in the Russian Superleague (RSL) and Kontinental Hockey League (KHL).

Kovalchuk was born in Kalinin (now Tver), a city roughly 180 kilometres northwest of Moscow, the second child and first son of Valeri and Lyubov.

[1] Valeri would later write a book detailing Kovalchuk's development as a hockey player, titled "From Tver to Atlanta" (Russian: «От Твери до Атланты») and published in 2004; he died in 2005 due to heart disease.

[1] At age seven, Kovalchuk was invited to join the Spartak Moscow youth school, which he went to every weekend, taking the train with his father.

[11] Entering his NHL rookie season in 2001–02, Kovalchuk scored 29 goals and 51 points despite missing 17 games with a season-ending shoulder injury.

Due to the 2004–05 NHL lockout, Kovalchuk returned to Russia, playing for both Ak Bars Kazan and Khimik Moscow Oblast of the Russian Superleague (RSL).

After the lockout, Kovalchuk and the Thrashers could not initially agree to a new contract, so he stayed in Russia, rejoining Khimik Moscow Oblast.

He played 11 games for the team, recording 8 goals and 13 points before returning to the Thrashers and NHL after signing a five-year, $32 million contract.

Kovalchuk scored one goal and one assist in his NHL playoffs debut as the team lost in the opening round to the New York Rangers in four games.

Near the beginning of the 2009–10 season, Kovalchuk scored the 300th and 301st goal of his NHL career in a 4–2 win during the St. Louis Blues' home opener on 8 October 2009.

[16] He was leading the NHL in goals several weeks into the season when he suffered a broken foot after blocking shot in a game against the San Jose Sharks on 24 October.

[18] A few days after Kovalchuk rejected the second contract offer, Waddell told him that he was going to be traded, rather than risk losing him to unrestricted free agency for nothing in the off-season, despite the fact that the Thrashers were still in the playoff race.

Atlanta received defenceman Johnny Oduya, rookie forward Niclas Bergfors, junior prospect Patrice Cormier and a first-round selection in the 2010 NHL Entry Draft in exchange for Kovalchuk and defenceman Anssi Salmela; the teams also traded second-round selections in the 2010 NHL Entry Draft.

On 10 February 2011, Kovalchuk scored the game-winning goal in a game over the Maple Leafs to give Jacques Lemaire the 600th win of his coaching career.

[21] Kovalchuk recorded a Gordie Howe hat trick – a goal, an assist, and a fight – on 4 February 2012, the second anniversary of his trade to the Devils, against the Philadelphia Flyers.

[24] Kovalchuk and the Devils won the 2011–12 Eastern Conference finals against the New York Rangers in six games, setting a Stanley Cup meeting with the Los Angeles Kings.

Arbitrator Richard Bloch heard the National Hockey League Players' Association (NHLPA)'s appeal and ultimately nullified the deal.

[28] As a result of the 2012–13 NHL lockout, Kovalchuk elected to sign a temporary contract with SKA Saint Petersburg of the Kontinental Hockey League (KHL) on 18 September 2012.

[29] In addition, Kovalchuk was the subject of criticism for not returning to the United States immediately after the lockout ended, instead electing to be one of two participating NHL players in the KHL All-Star Game (the other being Pavel Datsyuk).

Kovalchuk served as the captain of the Western Conference and returned to the United States to the Devils' training camp immediately after.

Several teams expressed interest, including the Los Angeles Kings, Vegas Golden Knights, San Jose Sharks and Boston Bruins.

On 23 June 2018, it was announced Kovalchuk and the Kings had agreed to a three-year contract, effective 1 July, with an average yearly value of $6.25 million.

Head coach John Stevens was fired and replaced by Willie Desjardins, who reduced Kovalchuk's ice time significantly.

Despite his contributions, the team was out of the playoff picture and after 22-game and 13-point tenure, Kovalchuk was traded on 23 February 2020 to the Washington Capitals in exchange for a third-round pick in the 2020 NHL Entry Draft.

[44] After two years away from professional hockey, Kovalchuk opted to return to his youth club of Spartak Moscow, signing a one-year contract on 6 December 2023.

The following year, Kovalchuk made his senior international debut with Russia at the 2002 Winter Olympics in Salt Lake City, during his rookie NHL season with the Atlanta Thrashers.

The following year, he led Russia to a second straight gold medal over Canada in the 2009 IIHF World Championship and was named the tournament MVP.

The Russian Hockey Federation was fined for the act, and while the IIHF determined Kovalchuk gave an "unmistakable head gesture" for his team to leave, he was not independently punished.