John Mustard was born in Newmarket, Ontario, Canada.
Mustard played for North Jersey for four years. In 2022-2023, Mustard had a big season, scoring 56 goals and 61 assists in 65 games.
John Mustard was selected by Waterloo in the 2023 USHL Draft. Mustard led the Black Hawks in goals and was named to the first-team,All-USHL Rookie Team in 2023-2024.
Mustard is committed to playing hockey at the University of Providence in 2025-2026.