New York Rangers

Duclair signed an entry-level contract with the Rangers on January 2, 2014.^[9] Because he waited until the beginning of 2014 to sign, under the NHL collective bargaining agreement, Duclair was exempt from a usual clause with rookie players in which they can be returned to their junior teams within the first 10 games of an NHL season without triggering the first year of their contract.^[10] He impressed head coach Alain Vigneault during the Rangers' 2014 training camp, but was not able to appear on their opening night roster until the team was under their 50-contract limit. General manager Glen Sather traded defenseman Steven Kampfer and forward Andrew Yogan to the Florida Panthers in exchange for Joey Crabb in order to accommodate a roster position for Duclair.^[11] He made his NHL debut on October 9, 2014, playing on a line with J. T. Miller and Lee Stempniak for a 3–2 Rangers victory over the St. Louis Blues.^[12][13] He recorded five points in his first seven NHL games, culminating in his first goal on October 27.^[14] The Rangers began the third period of that game down 3–0 to the Minnesota Wild, but Duclair scored the game-tying goal against Darcy Kuemper with just under four minutes left to play; 37 seconds later, Mats Zuccarello put the Rangers ahead 5–4 to win.^[15]

Duclair struggled to maintain his scoring output after his first goal: after recording one goal and five assists in his first nine games, he added only one more assist through the next nine.^[16] Although Vigneault and the Rangers were initially hesitant to send Duclair back to the Remparts, as he would have to remain there until the conclusion of their 2014–15 season,^[17] he was too young to play in the American Hockey League (AHL) and was returned to his junior team on January 5, 2015.^[18] After being returned to the Remparts, Duclair recorded 34 points in 26 QMJHL games,^[19] including seven points in his last four games before the 2015 playoffs.^[20] He added another 26 points in 22 playoff games before the Remparts were defeated by the Rimouski Océanic in Game 7 of the President's Cup series.^[21]

Arizona Coyotes

On March 1, 2015, while playing with the Remparts, Duclair was traded to the Arizona Coyotes (along with John Moore and two draft picks) in exchange for Keith Yandle and Chris Summers.^[22]

Arizona Coyotes general manager Don Maloney confirmed fan speculation by stating that he acquired Duclair from the New York Rangers in the hopes that he would develop line chemistry with a rookie Arizona already possessed, Max Domi.^[23] This was due to the fact that during the 2015 World Junior Ice Hockey Championship, Duclair and Domi both showed visible chemistry and were key components in leading Canada to gold.^[24]

On October 14, 2015, Duclair scored his first career NHL hat-trick in a 4–0 shut-out win against the Anaheim Ducks. Fellow rookie Max Domi pitched in a goal of his own and an assist on one of Duclair's goals.^[25] In Duclair's first full season in the NHL, he developed instant line chemistry with Domi, earning the duo the nickname "The Killer D's".^[26]

On January 19, 2017, Duclair was demoted to the team's American Hockey League (AHL) affiliate, the Tucson Roadrunners, due to a lack of production. On March 3, 2017, he returned to the Coyotes.

On January 4, 2018, it was reported that Duclair had requested to be traded from the Coyotes.^[27]

Chicago Blackhawks

On January 10, 2018, Duclair was traded (alongside defenceman Adam Clendening) to the Chicago Blackhawks in exchange for forwards Richard Pánik and Laurent Dauphin.^[28] His inconsistency carried over to the Blackhawks, after making an initial impact he finished the season scoreless in his last 14 games and finished the season appearing in 23 games for 8 points for Chicago.

On June 25, 2018, as a restricted free agent, Duclair was not tendered a qualifying offer by the Blackhawks and was released to explore free agency.^[29]

Columbus Blue Jackets

On July 5, 2018, Duclair signed a one-year, one-way contract worth $650,000 with the Columbus Blue Jackets.^[30] In 53 games for the team, Duclair recorded 11 goals and 19 points.

Ottawa Senators

On February 23, 2019, Duclair was traded to the Ottawa Senators (along with second-round picks in 2020 and 2021) in exchange for Ryan Dzingel and a seventh-round pick in 2019.^[31] Only a few days before the trade, Blue Jackets head coach John Tortorella publicly criticized Duclair, saying that Duclair "doesn't know how to play".^[32]

On June 17, 2019, Duclair signed a one-year contract with the Senators for the 2019–20 season worth $1.65 million.^[33] He immediately became one of Ottawa's top offensive players, recording 21 goals and 30 points in his first 38 games, leading the team in both categories. He was subsequently named as the Senators' representative for the 2020 NHL All-Star Game held on January 25, 2020, in St. Louis.^[34]

On June 8, 2020, Duclair became an inaugural executive board member of the Hockey Diversity Alliance, whose goal is to address intolerance and racism in hockey. ^[35]

In October 2020, Duclair fired his agent and took over contract negotiations with the Senators by himself, against the advice of GM Pierre Dorion. The two sides could not come to an agreement and the Senators declined to offer him a qualifying offer on a new contract, making him a free agent.

Florida Panthers

On December 17, 2020, Duclair signed as a free agent to a one-year, $1.7 million contract with the Florida Panthers.^[36]

On July 15, 2021, Duclair signed a three-year, $9 million contract extension with the Panthers. With four goals and seven assists in the 2023 Stanley Cup playoffs, Duclair would help the Panthers reach their first Stanley Cup Finals in 27 years.

San Jose Sharks

On July 1, 2023, due to salary cap considerations, Duclair was traded by the Panthers to the San Jose Sharks in exchange for Steven Lorentz and a fifth-round selection in 2025.^[37]

Tampa Bay Lightning

On March 7, 2024, Duclair was traded to the Tampa Bay Lightning in exchange for Jack Thompson and a 2024 third-round draft pick.^[38] Duclair scored the Lightning’s fifth goal of the evening and his first goal as a Bolt in his debut game on the team on March 9 against the Flyers.^[39]