Swedish Hockey League Liljegren made his
Swedish Hockey League debut on 3 December 2015 playing with
Rögle BK during the
2015–16 SHL season. Liljegren missed the first two months of the 2016–17 season after getting
mononucleosis. He later agreed with the Maple Leafs to a three-year, entry-level contract on 12 July 2017. Liljegren was assigned to the Maple Leafs'
American Hockey League (AHL) affiliate, the
Toronto Marlies, for their
2017–18 season. In his rookie season, he was the youngest defenceman in the AHL. That same season, the Marlies beat the
Texas Stars to win the
Calder Cup. Liljegren made his NHL debut with the Maple Leafs on 18 January 2020 in a 6–2 defeat against the
Chicago Blackhawks. He earned his first NHL point in his sixth NHL game; an assist in a 4–2 victory over the
Ottawa Senators. Liljegren scored his first
National Hockey League goal on 15 January 2022 against
Jordan Binnington of the
St. Louis Blues. On 27 June 2022, Liljegren signed a two-year $2.8 million contract with the Maple Leafs. He missed the beginning of the
2022–23 season with a
hernia. He played his first game of the season on 5 November against the
Boston Bruins. On 30 October 2024, Liljegren was traded to the
San Jose Sharks in exchange for
Matt Benning, a third-round pick in
2025, and a sixth-round pick in
2026. Liljegren was again traded to the
Washington Capitals on 6 March 2026 for a 4th-round pick in
2026. ==Personal life==