Henry Mews was born in Ottawa, Ontario, Canada.
Mews played for the Toronto Jr. Canadians at the U16 AAA level in the 2021-2022 season. He scored 14 goals and 64 assists in 52 games. At the 2022 OHL Cup, he recorded one goal and five points in six games.
Mews was selected 7th overall in the 2022 Ontario Hockey League (OHL) Priority Selection Draft. During his first season in the OHL. he produced 12 goals and 19 assists in 55 games.
In 2023-2024, Mews saw his production rise, scoring 15 goals and 46 assists in 65 games.