On 8 March 2014, Kuznetsov signed an entry-level contract with the Washington Capitals.
On 25 March, he scored his first career NHL goal, which happened to be a short-handed goal, against the Los Angeles Kings with under a minute left to tie the game; the Capitals, however, eventually lost 5–4 in the shootout.

On 23 April 2015, Kuznetsov scored the first and second Stanley Cup playoff goals of his career against the New York Islanders.
In the same game, he also had an assist in an eventual 5–1 Washington win.
On 27 April 2015, he scored the game-winning goal in Game 7 of the Eastern Conference Quarter-finals against the Islanders in the same series, advancing the Capitals to a Conference Semi-finals match-up against the 2014–15 Presidents' Trophy-winning New York Rangers.

During the 2015–16 season, Kuznetsov was named to his first All-Star Game as a replacement for Alexander Ovechkin, who pulled out due to a lower-body injury.

On 2 July 2017, the Capitals re-signed Kuznetsov (a restricted free agent) to an eight-year, $62.4 million contract worth $7.8 million per season.

In 24 playoff games in 2018, Kuznetsov had 12 goals and 20 assists for a total of 32 points, second only to Evgeni Malkin in 2009 among players in the last 25 seasons of Stanley Cup playoffs.
Kuznetsov's series-clinching overtime winner in Game 6 against Pittsburgh secured the Capitals’ first berth in the Eastern Conference Finals since 1998, ending years of playoff failure against the Penguins.
His four assists in Game 4 of the Stanley Cup Finals made him only the fourth NHL player to record that many in a finals game, the first in 22 years.
Kuznetsov led the league with 32 points in 24 appearances in the 2018 postseason, but lost to linemate and team captain Alex Ovechkin in the Conn Smythe Trophy competition.

"In helping deliver a championship Washington had wanted for more than 40 years, Kuznetsov was arguably the Capitals' most instrumental player.
The 26-year-old, fifth-year pro finished with a playoff-leading 32 points, including his 20th assist in Thursday night's series-clinching 4-3 win over the Vegas Golden Knights in Game 5."

— W.G. Ramirez, Associated Press
Members of the Professional Hockey Writers Association determined the winner of the Conn Smythe Trophy on a 5-3-1 basis, with the final tally determined by the NHL with ten minutes remaining in Game 5 of the finals.
All but two of the votes were cast for Washington Capitals players, with Kuznetsov and Ovechkin receiving inverse totals – Ovechkin took 13 first-place votes and five-second place, while Kuznetsov received five first-place votes and 13-second place.
Capitals goalie Braden Holtby was the third-place choice of 16 voters.
Golden Knights goalie Marc-André Fleury received the remaining two third-place votes.

Kuznetsov scored a power play goal and had three assists to power the Washington Capitals to a 5–2 win against the Vegas Golden Knights in a rematch of the 2018 Stanley Cup Final at Capital One Arena on October 10, 2018.
Of his performance, teammate T.J. Oshie said: "I think [Kuznetsov is] up there with the top five players in the League.
He just doesn't get the recognition for some reason.
But you come watch a game, there's certain players that get people out of their seats and it's a joy to watch."
Kuznetsov had the primary assist on each of the two goals by team captain Alexander Ovechkin, his 610th and 611th NHL career goals, surpassing Bobby Hull on the all-time goals list.
Of playing with Ovechkin, Kuznetsov said:
It's pleasure to play with him.
You may not understand right now but when you get older, you understand what kind of guy he is.
He's one of the best players in probably whole history.
He's gonna be in the Hall of Fame and maybe one of those pictures in Hall of Fame I'm gonna be somewhere around him just after we score.

On 14 September 2019, the NHL suspended Kuznetsov for three games for cocaine use after video surfaced on social media that showed Kuznetsov and another man sitting at a table that appeared to have lines of cocaine on it; the NHL termed the offens
On 8 March 2014, Kuznetsov signed an entry-level contract with the Washington Capitals. On 25 March, he scored his first career NHL goal, which happened to be a short-handed goal, against the Los Angeles Kings with under a minute left to tie the game; the Capitals, however, eventually lost 5–4 in the shootout.
On 23 April 2015, Kuznetsov scored the first and second Stanley Cup playoff goals of his career against the New York Islanders. In the same game, he also had an assist in an eventual 5–1 Washington win. On 27 April 2015, he scored the game-winning goal in Game 7 of the Eastern Conference Quarter-finals against the Islanders in the same series, advancing the Capitals to a Conference Semi-finals match-up against the 2014–15 Presidents' Trophy-winning New York Rangers.
During the 2015–16 season, Kuznetsov was named to his first All-Star Game as a replacement for Alexander Ovechkin, who pulled out due to a lower-body injury.
On 2 July 2017, the Capitals re-signed Kuznetsov (a restricted free agent) to an eight-year, $62.4 million contract worth $7.8 million per season.
In 24 playoff games in 2018, Kuznetsov had 12 goals and 20 assists for a total of 32 points, second only to Evgeni Malkin in 2009 among players in the last 25 seasons of Stanley Cup playoffs. Kuznetsov's series-clinching overtime winner in Game 6 against Pittsburgh secured the Capitals’ first berth in the Eastern Conference Finals since 1998, ending years of playoff failure against the Penguins. His four assists in Game 4 of the Stanley Cup Finals made him only the fourth NHL player to record that many in a finals game, the first in 22 years. Kuznetsov led the league with 32 points in 24 appearances in the 2018 postseason, but lost to linemate and team captain Alex Ovechkin in the Conn Smythe Trophy competition.
"In helping deliver a championship Washington had wanted for more than 40 years, Kuznetsov was arguably the Capitals' most instrumental player. The 26-year-old, fifth-year pro finished with a playoff-leading 32 points, including his 20th assist in Thursday night's series-clinching 4-3 win over the Vegas Golden Knights in Game 5."
— W.G. Ramirez, Associated Press
Members of the Professional Hockey Writers Association determined the winner of the Conn Smythe Trophy on a 5-3-1 basis, with the final tally determined by the NHL with ten minutes remaining in Game 5 of the finals. All but two of the votes were cast for Washington Capitals players, with Kuznetsov and Ovechkin receiving inverse totals – Ovechkin took 13 first-place votes and five-second place, while Kuznetsov received five first-place votes and 13-second place. Capitals goalie Braden Holtby was the third-place choice of 16 voters. Golden Knights goalie Marc-André Fleury received the remaining two third-place votes.
Kuznetsov scored a power play goal and had three assists to power the Washington Capitals to a 5–2 win against the Vegas Golden Knights in a rematch of the 2018 Stanley Cup Final at Capital One Arena on October 10, 2018. Of his performance, teammate T.J. Oshie said: "I think [Kuznetsov is] up there with the top five players in the League. He just doesn't get the recognition for some reason. But you come watch a game, there's certain players that get people out of their seats and it's a joy to watch." Kuznetsov had the primary assist on each of the two goals by team captain Alexander Ovechkin, his 610th and 611th NHL career goals, surpassing Bobby Hull on the all-time goals list. Of playing with Ovechkin, Kuznetsov said:
It's pleasure to play with him. You may not understand right now but when you get older, you understand what kind of guy he is. He's one of the best players in probably whole history. He's gonna be in the Hall of Fame and maybe one of those pictures in Hall of Fame I'm gonna be somewhere around him just after we score.
On 14 September 2019, the NHL suspended Kuznetsov for three games for cocaine use after video surfaced on social media that showed Kuznetsov and another man sitting at a table that appeared to have lines of cocaine on it; the NHL termed the offens
Evgeny Kuznetsov