Harry Amass was born on 16 March 2007 in England and began his development at Watford, joining the club at the age of nine. He attracted attention from top-flight clubs while still a teenager, and in August 2023 Manchester United confirmed his signing on a four-year deal, having beaten Chelsea to his signature earlier that year.
Amass made his senior debut for Manchester United on his 18th birthday, 16 March 2025, coming on as a substitute against Leicester City at the King Power Stadium. He made his first senior start less than a month later against Newcastle United. That same season, United reached the UEFA Europa League final, finishing as runners-up, and Amass was named the club's Jimmy Murphy Young Player of the Year for 2024–25.
In September 2025 he joined Championship side Sheffield Wednesday on loan, making 21 appearances and scoring one goal — a long-range strike away to Southampton — before returning to United in January 2026. He subsequently joined Norwich City on loan in January 2026, though an injury sustained in training cut that spell short.
At international level, Amass represented England at under-15 and under-16 level, helping the U16 side win a UEFA Development Tournament in Cyprus in February 2023. He was part of the England squad at the 2024 UEFA European Under-17 Championship and converted his penalty in the quarter-final shootout loss to Italy. He made his England U18 debut against Portugal in September 2024.
A left-back with a willingness to press forward and a reputation for tough tackling, Amass is viewed by Manchester United as a long-term option at left-back.