York earned stability in the NHL when he signed a five-year, $25.75 million contract with the Philadelphia Flyers on July 7, 2025, after he built off what was his best NHL season (30 points; 10 goals, 20 assists in 2023-24) with 17 points (four goals, 13 assists) while averaging 20:47 of ice time in 66 games. Among Flyers defensemen, York was second in average ice time, tied for third in goals, fourth in assists and fifth in points, and the lone skater at his position to play all 82 games.

The following season, York increased his numbers to 22 assists, 26 points, a plus-5 rating and an average ice time of 23:32. His goal with 2:28 left in overtime gave the Flyers a 1-0 win against the Pittsburgh Penguins in Game 6 of the Eastern Conference First Round on April 29, 2026. He became the third defenseman in the NHL modern era (since 1943-44) to score his first Stanley Cup Playoff goal in OT of a series-clinching game, joining Chris Tanev in Game 4 of the 2020 Stanley Cup Qualifiers and Brooks Orpik in Game 6 of the 2013 Eastern Conference Quarterfinals.

York was chosen by Philadelphia in the first round (No. 14) of the 2019 NHL Draft, made his NHL debut against the Washington Capitals on May 7, 2021, and scored his first NHL goal against the New York Rangers on Jan. 15, 2022. He played two seasons at the University of Michigan from 2019 to 2021, where he was named to the Big Ten All-Freshman Team and a Big Ten Rookie of the Year finalist. His 20 points (four goals, 16 assists) with a plus-13 rating in 24 games as a sophomore earned him Big Ten Defenseman of the Year honors and a place on the First Team All-Big Ten.

He also played for USA Hockey's National Team Development Program under-18 team and became the first player in NTDP history with seven points (three goals and four assists) in one game against Youngstown on Jan. 15, 2019. His 103 points (22 goals, 81 assists) in 122 games from 2017-19 made him the second NTDP defenseman to reach the 100-point milestone (J.D. Forrest).

Internationally, York won gold as captain of the United States at the 2021 IIHF World Junior Championship. He's also a gold medalist at the 2017 World Under-17 Hockey Challenge, and earned sliver at the 2018 IIHF U-18 World Championship and bronze at the 2019 World Under-18s and the 2020 IIHF World Juniors.