The Russian club did not disclose contract details, only saying on their website (www.ska.ru) that the forward for the NHL's New Jersey Devils would wear the number 17 jersey.
Kovalchuk, 29, joins NHL Most Valuable Player Evgeni Malkin of the Pittsburgh Penguins and former All-Star defenceman Sergei Gonchar of the Ottawa Senators, who both signed for KHL rivals Metallurg Magnitogorsk on Sunday, in the Russian league.
The exodus of top NHL talent to Russia is widely expected to continue since the North American league imposed a league-wide lockout after failing to reach a new collective bargaining agreement with the players' union over the weekend.
The ambitious KHL, formed three years ago with the help of Russian President Vladimir Putin, has jumped at the chance to recruit some of the world's best players, hoping it would help the fast-growing league emerge from the shadows of the NHL.
For example, Magnitogorsk has given Malkin a hero's welcome despite the fact that the Russian defected to the United States during the team's training camp in Finland in 2006. The Russians then threatened to go to a U.S. court to seek compensation from Pittsburgh before settling the case with the NHL club.
Despite signing a peace agreement with the NHL last year, KHL boss Alexander Medvedev has been eager to bring back the best home-grown players, saying such a move would greatly increase the popularity of the league both at home and abroad.
Russia's national coach Zinetula Bilyaletdinov also welcomed the opportunity to see the country's elite players in person rather than watch them on TV, saying it would help mould the best possible team for the 2014 Sochi Olympics.
Likewise, most Russian players are quick to take advantage of the work-stoppage in the NHL and sign lucrative deals with wealthy KHL clubs.
Kovalchuk, who inked a record 15-year, $100 million contract with New Jersey in 2010, was expected to make close to $8 million in St. Petersburg if he plays the full season for SKA.
Washington Capitals forward Alexander Ovechkin, one of the NHL's highest-profile players, is reportedly mulling a similar offer from his former club Dynamo Moscow or an even bigger one from rich city rivals CSKA, backed by the state-owned oil company Rosneft.
The Russian league has repeatedly stated that it wants to bring only the best players from the NHL, imposing strict eligibility rules for those looking to move across the Atlantic.
To be eligible, a player must have either previous KHL experience, played no fewer than 150 NHL games over the last three seasons, or represented his country at one of the last two world championships or the Olympics.
Each KHL team is also restricted to signing only three NHL players, with Magnitogorsk, coached by ex-Carolina Hurricanes boss Paul Maurice, becoming the first to use up its quota.
In addition to Malkin and Gonchar, the team from the Urals, owned by a major Russian steel mill, signed another home-grown talent, Nikolai Kulemin of the Toronto Maple Leafs, on Monday.
However, not everyone in Russia was happy with the work-stoppage in the NHL.
"I don't really care if there is a lockout or not," Leonid Vaisfeld, the boss of cash-strapped Metallurg Novokuznetsk, was quoted as saying by local media. "Taking into account our modest financial resources, it will have little effect on our club."