McTavish started playing against professional competition earlier than expected.

With the Ontario Hockey League canceling its season in 2020-21 due to concerns surrounding the coronavirus, McTavish played on loan with Olten EHC in the Swiss League, the second-tier league in Switzerland.

It was a return home for McTavish, who was born in Zurich while his father, Dale McTavish, was playing professional hockey in the country.

After he scored 11 points (nine goals, two assists) in 13 regular-season games and seven points (two goals, five assists) in four playoff games, McTavish came back to North America to play for Canada at the 2021 IIHF Under-18 World Championship. In the tournament, he scored 11 points (five goals, six assists) to help Canada win the title for the first time since 2013.

Those performances were enough to impress the Anaheim Ducks, who selected him with the No. 3 pick in the 2021 NHL Draft. He signed a three-year, entry-level contract with the Ducks on Aug. 13, 2021 and scored his first goal in his NHL debut, a 4-1 win against the Winnipeg Jets on Oct. 13. His 43 points (17 goals, 26 assists) in 80 games ranked fourth in Ducks history for single-season points by a rookie.

McTavish led the 2022 IIHF World Junior Championship with eight goals and 17 points. Canada's captain tied Wayne Gretzky (1978) and Eric Lindros (1991) for the second-most points by a Canada player at the WJC, one point behind the record held by Dale McCourt (1977) and Brayden Schenn (2011), and was named the tournament's best forward and most valuable player. The lasting memory will be his remarkable save 2:09 into overtime of the championship game, when he batted a puck down on the goal line, and then cleared it out of trouble.

McTavish signed a six-year contract with the Ducks on Sept. 27, 2025, after setting single-season NHL career highs in goals (22), assists (30), points (52), shots (180) and time on ice per game (16:53). He was the fifth-youngest Ducks skater with 50 points in a season and the second player in team history to score 50 goals before turning 21, joining Paul Kariya.