In 2004, Kovalev participated in the Russian Senior Championship for the first time, reached the finals, and won the gold medal in the team event.

Kovalev admitted that he felt forced to leave the national team because of the intense competition between him and others boxers such as Artur Beterbiev (to whom he lost 24–25).

In July 2011, Kovalev won his first North American Boxing Association belt in a 10-round fight with Douglas Otieno from Kenya.

His next bout against Grover Young was controversial: during the second round, Kovalev threw a left hook that the referee declared an illegal blow to the back of the head.

Kovalev met Darnell Boone in the ring for the second time and knocked him out in the second round; the win led him to be signed on to Main Events boxing.

[7] On 19 January 2013, Kovalev faced the former World Boxing Association (WBA) light-heavyweight champion Gabriel Campillo.

Kovalev took advantage of Campillo's faltering defense and knocked him down with a left hook, one of three knockdowns in the round.

[8][9] On 17 August 2013, Kovalev fought Nathan Cleverly for the World Boxing Organization (WBO) light-heavyweight title.

[15] On 29 March 2014, Kovalev defended his title against undefeated Cedric Agnew (26–0, 13 KOs) at the Adrian Phillips Ballroom at Boardwalk Hall in Atlantic City.

Although Agnew was not known to many boxing fans at the time, he won against Yusaf Mack, Daniel Judah, and Otis Griffin.

Although the figures were down from the Kovalev vs. Sillakh bout, the fight was televised at the same time as Wisconsin vs. Arizona, competing to reach the Final Four of the NCAA's college basketball tournament.

On 2 August 2014, Kovalev defended his WBO title against undefeated Australian contender Blake Caparello (19–0–1, 6 KOs) at the Revel Casino Hotel in Atlantic City, New Jersey, and it was televised on Boxing After Dark.

Main Events spokesperson Kathy Duva believed there was a loss of focus due to building pressure, which was why Kovalev was dropped by Caparello.

[15] On 25 July 2015, Kovalev fought French boxer Nadjib Mohammedi (37–3, 23 KOs) at the Mandalay Bay Resort & Casino in Las Vegas.

The fight was unlikely to happen as Beterbiev was advised by Al Haymon, and performed on Premier Boxing Champions, who were banned by HBO.

[42] On 16 June 2016, it was announced that a contract had been signed between Kovalev and Ward (30–0, 15 KOs), and that the match would take place at the T-Mobile Arena in Las Vegas on 19 November 2016.

[43] Kovalev lost a closely contested controversial decision with all the judges scoring the fight 114–113 in favor of Ward.

"[47] Many boxing experts have applauded the decision: Paulie Malignaggi noted the high degree of difficulty both fighters faced that night and doubted the prospect of a one-sided affair in the case of a rematch, though he concluded that Kovalev faded late in the fight;[48] promoter Eddie Hearn added that Kovalev lacked a sense of urgency after the halfway point;[49] Gennady Golovkin's trainer, Abel Sanchez, noticed how Kovalev allowed Ward on the inside and as a result was worn down.

[58] On 4 April, Roc Nation Sports and Main Events confirmed that terms were agreed for the rematch to take place on HBO PPV.

[59][60] The Las Vegas Sun confirmed the bout would take place at the Mandalay Bay Events Center.

[69][70] Kovalev spoke to reporters in Russia on 27 June 2017, and confirmed that he would be making changes to his team, which included a new head trainer, meaning he would part ways with John David Jackson, and a new specialist.

[72][73] On 25 November, Kovalev appeared on Boxing After Dark against light-heavyweight contender Vyacheslav Shabranskyy (19–1, 16 KOs) in a scheduled ten-round bout that took place at The Theater at Madison Square Garden in New York City.

[76] On 12 October, Main Events asked the WBO to sanction the fight for their vacant title, following Ward's retirement from boxing.

[82] Immediately after defeating Shabranskyy, Kovalev stated that he would return to The Theater on 3 March 2018 in the hopes of joining a unification fight with belt holders Artur Beterbiev (IBF), Dmitry Bivol (WBA), and Stevenson (WBC).

[83][84] On 18 December, ESPN reported a deal was close to being made for Kovalev to defend his WBO title against IBO titleholder Igor Mikhalkin (21–1, 9 KOs), who was on a 10-fight win streak.

[89] On 18 March, a deal was made for Kovalev to defend his WBO title against Browne at the Hulu Theater at Madison Square Garden on HBO.

[106] Kovalev regained the WBO title after defeating Álvarez by a 12-round unanimous decision and became a three-time light-heavyweight titleholder.

[110] After 11 rounds, Kovalev knocked out Yarde with a straight left jab, ending the fight via TKO and retaining his WBO and ESP light-heavyweight titles.

[111][112][113][114] Less than three months after beating Yarde, Kovalev faced unified middleweight champion Canelo Álvarez on 2 November 2019, who made his debut in the light-heavyweight division.

He was charged with assault likely to cause great bodily injury, which is a felony; he pleaded not guilty on 27 August 2018, and he was released on $50,000 bail.