Junior The
Lethbridge Hurricanes of the
Western Hockey League (WHL) selected Cozens in the first round, 19th overall, of the 2016 WHL bantam draft. He signed with the team that May, but because he was below the WHL's age minimum for the upcoming
2016–17 season, he played for the Yale Hockey Academy in
Abbotsford, British Columbia, instead. After three games, he returned to Yale, where his 57 points (27 goals and 30
assists) in 30 games were tied for the CSSHL Midget Prep league lead. Cozens added another two goals and four points in three CSSHL playoff games, and once the Yale season ended, he rejoined Lethbridge for the WHL postseason. There, he had three goals and eight points in 12 playoff games before the Hurricanes were eliminated by the
Regina Pats in the Eastern Conference Championship series. Cozens returned to the Hurricanes for a full rookie season in
2017–18. After recording 13 points in as many games, including a five-game point streak and a three-point game against the
Medicine Hat Tigers, he was named the WHL Rookie of the Month for October 2017. Cozens recorded his first WHL
hat-trick on January 13, leading Lethbridge to a 5–2 victory over the
Kootenay Ice. That performance, combined with three goals and six points in a two-game series against the
Red Deer Rebels, earned Cozens WHL Player of the Week honours for the week ending January 14. In his first full season of junior ice hockey, Cozens posted 22 goals and 53 points in 57 regular-season games, and he received the
Jim Piggott Memorial Trophy as the top rookie in the WHL. The Hurricanes faced the Rebels in the first round of 2018 WHL playoffs, and Cozens recorded his first postseason hat-trick in the second game of the series. Although the Hurricanes lost to the
Swift Current Broncos in the WHL Eastern Conference Championship series, Cozens was named the WHL Rookie of the Month for April 2018 after recording seven goals and 13 points in 16 playoff games. Cozens was a finalist for the
CHL Rookie of the Year award at the end of the season, a title that ultimately went to
Alexis Lafrenière of the
Rimouski Océanic. At the start of the
2018–19 season, the
NHL Central Scouting Bureau ranked Cozens, who had five goals and ten points in four games, an "A"-level
prospect. His 14 points in 10 games led Lethbridge in scoring, and Cozens was one of three Lethbridge players to represent Team WHL at the 2018
CHL Canada/Russia Series. On November 23, Cozens recorded the first six-point game of his junior hockey career, scoring a hat-trick and recording an additional three assists in Lethbridge's 8–4 victory over the
Brandon Wheat Kings. In January, Cozens was appointed the
captain of Team Cherry at the 2019
CHL/NHL Top Prospects Game. Cozens finished his sophomore junior hockey season with 34 goals and 84 points in 68 regular-season games, and the NHL Central Scouting Bureau ranked him the No. 5 prospect among all North American skaters. He added an additional four goals and eight points in seven playoff games, but the
Calgary Hitmen eliminated the Hurricanes in a winner-takes-all game seven of their opening-round playoff series. On June 21, the
Buffalo Sabres of the
National Hockey League (NHL) selected Cozens seventh overall in the
2019 NHL entry draft. He was the first Yukon-born player ever taken in the first round of the NHL draft. Cozens signed a three-year,
entry-level contract with the Sabres on July 15, 2019. After attending Buffalo's training camp, Cozens returned to Lethbridge for the
2019–20 season. After recording 10 goals and 17 points through the first 13 games of the season, Cozens was named an alternate captain for Team WHL at the 2019 Canada/Russia Series. Cozens told reporters that he wanted to "stay at an NHL level" during the Hurricanes' season, and by December 11, he led the team with 42 points (19 goals and 23 assists) in 28 games. Halfway through the season, Cozens and Ty Prefontaine were named co-captains for the Hurricanes. By the time that
concerns surrounding the COVID-19 pandemic forced the WHL to indefinitely postpone the 2019–20 season, Cozens led Lethbridge with 38 goals and 85 points in 51 games. Cozens was named to the WHL Eastern Conference First All-Star Team at the end of the season, and he was the runner-up for the
Four Broncos Memorial Trophy, an award which went to
Adam Beckman of the
Spokane Chiefs. Cozens finished his WHL career with 95 goals and 223 points in 179 regular-season games, as well as 14 goals and 29 points in 35 postseason games.
Professional Buffalo Sabres (2021–2025) Cozens joined the Sabres for the
2020–21 season, making his NHL debut on January 14, 2021. Although Buffalo lost the game 6–4 to the
Washington Capitals, Cozens recorded his first NHL point with an assist on
Tobias Rieder's second-period goal. He scored his first goal on January 22, also against the Capitals. Although Cozens's goal tied the game 2–2, Washington ultimately won the game 4–3 in a
shootout. In February, Cozens was one of several Buffalo skaters to miss time in COVID-19 protocols. Drafted as a
centre, Cozens spent most of his rookie NHL season on the
wing, only returning to the centre to fill in for an injured
Jack Eichel in March. Cozens suffered additional setbacks with two separate upper body injuries: after missing four games at the beginning of March, he sat out an additional six games following a hard
check from
Philippe Myers of the
Philadelphia Flyers on March 29. He had a strong April, assisting seven times in an eight-game span, and finished his rookie NHL season with four goals and 13 points in 41 games. With
Sam Reinhart's offseason departure and Eichel indefinitely sidelined due to a dispute with the Sabres' front office, an opportunity opened for Cozens to become a top-six centre for Buffalo during the
2021–22 season. He recorded the first multi-goal game of his career on November 12, scoring twice in a 3–2 win over the
Edmonton Oilers. Cozens entered an extended slump in the stretch of the season, going without a goal between February 25 and April 5. He finally broke the drought after 17 games with a
power play goal in Buffalo's 4–2 win against the
Carolina Hurricanes. Cozens finished his first full NHL season with 13 goals and 38 points in 79 games. All but two of those goals came before the midseason
NHL All-Star Game break. Cozens told reporters after the season that when his offensive production faltered, he switched his focus to improving his defence. On February 7, 2023, the Sabres signed Cozens to a 7-year contract extension worth $49.7 million.
Ottawa Senators (2025–present) On March 7, 2025, the Sabres traded Cozens,
Dennis Gilbert, and a second-round pick in the
2026 NHL entry draft to the
Ottawa Senators in exchange for
Josh Norris and
Jacob Bernard-Docker. Playing on a line with
Drake Batherson and
David Perron, Cozens made an immediate impact with the Senators, recording three goals and seven points in his first eight games. He recorded his 200th career point on March 11, with a goal in Ottawa's 5–2 victory over the
Philadelphia Flyers. In 21 regular season games with the Senators, Cozens recorded five goals and 16 points. Cozens made his postseason debut in the first round of the
2025 Stanley Cup playoffs, recording a goal and an assist in six games against the
Toronto Maple Leafs. Going into the
2025–26 season, Cozens spent two months working with
Sam Gagner, the Senators' director of player development. Despite posting 10 points in the first 11 games of the season, Cozens struggled defensively, with a –10 plus–minus. He recorded two three-point games in December, one on December 11 in a 6–3 victory over the Columbus Blue Jackets and then again on December 21, in a 6–2 win over the Boston Bruins. He tallied another three-point game on January 14, 2026, in an 8–4 victory over the New York Rangers. Cozens scored his 100th NHL goal on January 31, in a 4–1 win against the
New Jersey Devils. At the end of February on February 28, Cozens added another three-point night, scoring twice and assisting on another in a 5–2 victory over the Toronto Maple Leafs. The Senators made the playoffs again, but were swept in the first round by the
Carolina Hurricanes. Cozens registered two goals in the four games. ==International play==