John grew up in Upstate New York where he began playing both ice and roller hockey. He attended prep school at Salisbury School in Connecticut where he played one season before joining the US National Development Program. John played his collegiate hockey at the University of Michigan, playing three NCAA seasons for the Wolverines. He represented the United States at the U17, U18 and U20 level helping his team to a gold medal at the 2017-18 World Under-17 Hockey Challenge. John was selected by the Boston Bruins in the 1st round of the 2019 NHL Entry Draft. Following his third collegiate season, John began his pro career finishing the season with the Providence Bruins of the AHL contributing 5 points in 9 games. He signed his entry-level contract in May of 2022. John made his NHL debut with the Boston Bruins on October 11, 2023.