Following the 2017–18 KHL season, Samsonov embarked on his NHL career by signing a three-year, entry-level contract with the Washington Capitals.

Samsonov participated in the Capitals training camp but was re-assigned to their American Hockey League (AHL) affiliate, the Hershey Bears, prior to the start of the 2018–19 season.

He eventually made his NHL debut the following season while playing in a primary backup role to starter Braden Holtby.

[5] Samsonov was ranked as the top European Goalie eligible for the 2015 NHL Entry Draft and drew comparisons to Andrei Vasilevskiy.

[6] Following the draft, Samsonov returned to the Metallurg Magnitogorsk for the 2015–16 season where he posted a 6–4–3 record with a 2.04 goals against average and .925 save percentage through 19 games.

[7] He played a backup role during the 2016 Gagarin Cup playoffs but made six appearances and posted a 2–2–0 record with a 2.29 GAA and a .916 save percentage.

Due to the language barrier, Capitals senior director of communications Sergey Kocharov was on the ice when Samsonov was conducting drills during their Development Camp.

[12] After the signing, the Capitals traded Philipp Grubauer to the Colorado Avalanche leaving a backup goaltending spot available which Samsonov was expected to eventually fill.

Off the ice, he hired an English tutor to assist with the language barrier and worked on adjusting to North American rink sizes.

[13] In September, Samsonov participated in the Capitals training camp but was re-assigned to their American Hockey League (AHL) affiliate, the Hershey Bears, prior to the start of the 2018–19 season.

[19] One of the items he worked on was changing his form from playing on his knees to standing taller in net, the Capitals’ preferred positioning.

[22] As a result of his play over this time period, Samsonov led all rookie goaltenders with 15 wins and was projected to replace Holtby who could become an unrestricted free agent.

[31] Samsonov was removed from COVID protocol on 8 February but spent time with the Hershey Bears on a conditioning stint for an extra 20 days.

[34] Between injuries and being in and out of coronavirus protocol, Samsonov missed some time, including the first two games of the 2021 Stanley Cup playoffs against the Boston Bruins.

Samsonov returned for Game 3 but misplayed the puck during double overtime and turned it over to Craig Smith, who took advantage and scored the game-winning goal, giving the Bruins a 2–1 series lead.

[38] On 6 April 2022, Samsonov made his fourth start in 15 games and stopped 25 of 28 shots by the Tampa Bay Lightning to mark his first 20-win season in the NHL.

[39] As a free agent from the Capitals, Samsonov opted to sign a one-year, $1.8 million contract for the 2022–23 season with the Toronto Maple Leafs on 13 July 2022.