After agreeing to a contract with the Knights, Zadorov began his major junior career in the Ontario Hockey League (OHL) in the 2012–13 season, joining fellow Russian Vladislav Namestnikov. After adapting to the differing style and dimensions of the North American game, Zadorov assumed a top pairing role and led All-Rookie defencemen in plus–minus with +33, and finishing second in scoring with 6 goals and 25 points in 63 games.[4] Earning a roster spot in the 2013 CHL Top Prospects Game, Zadorov helped the Knights claim the OHL championship to advance to the Memorial Cup.[3] As he was selected to the OHL First-All Rookie Team, he scored the game-winner in the opening game against the Western Hockey League's Saskatoon Blades before losing in the semi-finals.[5] Zadorov's impressive season was noted as he was selected with the Buffalo Sabres's second first-round pick, 16th overall, in the 2013 NHL entry draft.[6]
Buffalo Sabres
Zadorov attended his first rookie and NHL training camp and after his third pre-season contest he was signed by the Sabres to a three-year, entry-level contract on 26 September 2013.[7] Under the assessment of head coach Ron Rolston, he made the Sabres' opening night roster to begin the 2013–14 season.[8] Zadorov sat out the first ten games before he made his NHL debut in a 4–2 defeat to the Colorado Avalanche on 19 October.[9] In just his second game, against the Boston Bruins on 23 October, Zadorov scored on his first shot in the NHL, against Chad Johnson.[10] In so doing, he became the youngest Sabres defenceman in franchise history to achieve the feat.[11]
With the Sabres cleaning out the front office and coaching staff, and with an imperative to rely less on the youth from new head coach Ted Nolan, on 19 November, Zadorov was returned to junior with the London Knights after seven NHL games played.[12] He played out the remainder of the season with the Knights, assuming a top-pairing role in surpassing his rookie season totals in points (30) in half the number of games (36), earning a selection to the OHL Second All-Star Team.[13]
Despite a benching during the rookie pre-season tournament in Traverse City, Michigan, Zadorov rebounded to have a strong training camp to make the Sabres' opening-night roster in the 2014–15 season as a permanent addition to the blueline.[14][15] He initially only saw limited playing time as a rotational option to the third-pairing under Ted Nolan and was primarily on the team for practice only (he was not yet eligible for the American Hockey League and a tie-up involving Zadorov's KHL rights prevented him from being returned to juniors).[16] Zadorov's playing time soon increased in the season as the team's coaching staff decided to keep Zadorov regardless of his junior situation.[17][18] In developing a shut-down role through his physicality, Zadorov showed offensive glimpses, collecting his first multi-point game in scoring an overtime marker in a 4–3 victory over the Florida Panthers on 13 December 2014.[19] Zadorov also became the youngest Sabres defenceman in history to score an overtime winner.[20] Zadorov showed his youth by suffering two team suspensions over the course of his rookie campaign, after returning late from holiday over the All-Star break and later oversleeping through a team practice.[21] Despite a lowly year for the Sabres, Zadorov led the blueline in plus–minus and finished with 3 goals, 12 assists in 60 games.[22]
Colorado Avalanche
At the 2015 NHL entry draft, Zadorov was traded as a central piece by the Sabres in a package that also included Mikhail Grigorenko, J. T. Compher and the 31st pick in the draft to the Colorado Avalanche in exchange for Ryan O'Reilly and Jamie McGinn on 26 June 2015.[23] Upon learning about the trade, Zadorov said he was happy since he "knew about this organization...it’s always nice to play for a GM who's actually been here and knows what it’s like for the players when you’re playing and working hard."[24] He began the season with the team but was reassigned to their American Hockey League (AHL) affiliate, the San Antonio Rampage, in order to improve his game. When speaking of the decision, General Manager Joe Sakic said "for a young man in that position, he needs to play a ton and work on his confidence. He’ll go down and play as much as he can and keep learning that way. The only way you can get better is by playing a lot at a young man’s age."[25] At the time of his reassignment, he had recorded two assists in 11 games and been a healthy scratch for four consecutive games.[26] Zadorov remained in the AHL until he earned his first recall on 13 January alongside Chris Bigras after Nate Guenin was placed on waivers.[27] His stay in the NHL was short-lived, however, as he was reassigned to the Rampage on 23 January after Erik Johnson was activated from injured reserve.[28]
The following year, Zadorov made the Avalanche's lineup out of training camp and remained on their roster for the entirety of the 2016–17 season. In February 2017, Zadorov collided with forward Mikko Rantanen during practice and suffered a season-ending fractured ankle injury. At the time of the incident, he had recorded 10 assists and no goals in 56 games.[29] Prior to the start of the 2017–18 season, the Avalanche signed him to a two-year contract extension to remain with the team.[30] He was also medically cleared to play but was late returning for the Avalanche's 2017 training camp due to Visa issues.[31] Entering his third season with the team, Zadorov broke one franchise record and set his own new career-high totals in goals, assists, and points. On 22 March, Zadorov surpassed the previous Avalanche record for most hits in a single game with 15, which was also the third-most hits by an NHL player since 1998–99. By the conclusion of the season, Zadorov led the league with 278 hits and recorded a career-best seven goals, 13 assists, and 20 points.[32]
On the heels of his most successful season, Zadorov underwent shoulder surgery in the off-season and was expected to miss participating in the Avalanche's 2018 training camp.[33] In spite of this, Zadorov participated in the Avalanche's training camp wearing a non-contact jersey before being cleared as a full participant in practice on 20 September.[34] He ended his fourth year campaign playing in 70 regular season games and recording seven goals, seven assists, and accumulating 75 penalty minutes. As a result, the Avalanche re-signed Zadorov, who was expected to become a restricted free agent, to a one-year, $3.2 million contract.[35]
With his newest contract signed, Zadorov returned to the Avalanche for their 2019 training camp, although he left on the third day due to an injury.[36] He was listed as day-to-day with a lower-body injury before fully returning to team practice on 24 September, with fellow injured players Pierre-Édouard Bellemare and Erik Johnson.[37] During the shortened 2019–20 season, Zadorov suffered a facial fracture as a result of taking a puck to the face during a game against the Nashville Predators.[38] He returned to the Avalanche's lineup three games later after recovering from surgery to heal his broken jaw.[39] As the Avalanche qualified for the 2020 Stanley Cup playoffs, they faced off against the Arizona Coyotes in the First Round. They beat the Coyotes in five games and Zadorov recorded his first playoff goal in the 7–1 Game 5 win.[40] During their Second Round contests against the Dallas Stars, Zadorov passed Matt Duchene for 74th place on the franchise playoff points list.[41] In the second-round series against the Dallas Stars, despite injuring his arm, Zadorov was able to play through pain, and following the Game 7 defeat to the Stars opted to undergo surgery. He finished the playoffs with 3 goals and 5 points through 15 games. On 8 October 2020, Zadorov as a restricted free agent was tendered a qualifying offer by the Avalanche.[42]
Chicago Blackhawks
On 10 October 2020, Zadorov's five-year tenure with the Avalanche ended as he was dealt alongside Anton Lindholm to the Chicago Blackhawks in exchange for Brandon Saad and Dennis Gilbert. Prior to the trade, he had accepted his one-year, $3.2 million qualifying offer for the 2020–21 season.[43] In his lone season with the Blackhawks, Zadorov appeared in 55 out of 56 regular season games, registering 1 goal and 8 points from the blueline and was unable to help Chicago return to the playoffs.
Calgary Flames
On 28 July 2021, Zadorov – an impending restricted free agent – had his negotiation rights traded to the Calgary Flames in exchange for a 2022 third-round pick.[44] On 20 August, he agreed to a one-year, $3.75 million contract, avoiding arbitration.[45] On 12 April 2023, Zadorov recorded his first career NHL hat-trick in a 3–1 win over the San Jose Sharks.[46]
On 10 November 2023, following a loss to the Toronto Maple Leafs, it was reported that Zadorov had requested a trade.[47][48]
Leaving the Canucks as a free agent having been unable to come to terms on an extension at the conclusion of his contract, Zadorov returned to the Eastern Conference in signing a six-year, $30 million deal with the Boston Bruins on 1 July 2024.[51]
Zadorov married his wife in 2015.[53] They have two daughters, who were born in 2017 and 2020.[54] In the offseason, Zadorov resides in Miami, Florida.[55]
In September 2023, Zadorov spoke with Russian journalist Yury Dud about politics, including the Russo-Ukrainian War, which he opposes. Zadorov said that Russian NHL players had attempted to form a joint statement about the war, but failed to reach any agreement.[56][57] Speaking to Canadian media the day after the interview's release, Zadorov said: "I probably can't go back [to Russia] anytime soon."[58] In May 2024, Iain McIntyre of Sportsnet called Zadorov a "player without a country".[55]