The Premier League clubs did not reveal the transfer fee, but British media reported Leeds will pay around 40 million pounds plus bonuses. The transfer makes the 23-year-old the most expensive British goalkeeper in history.
Trafford arrives at Elland Road after spending last season back at Manchester City, where he made 17 appearances in all competitions. The England international was also included in Thomas Tuchel's squad for the 2026 FIFA World Cup.
The goalkeeper said he is delighted to complete the move and is eager to begin preparing for the new season with his new team.
"I know my own abilities. I go out and try as hard as I can and have as much fun as I can," Trafford said.
"I am really excited and just really happy that it is finally done. I can get onto preparing for the new season and can focus on getting in with everyone next week."
Trafford came through Manchester City's academy before gaining valuable experience during loan spells at Accrington Stanley and Bolton Wanderers. He joined Burnley on a permanent transfer in 2023 before returning to City last year.
Despite his return, Trafford found regular first-team opportunities limited as Gianluigi Donnarumma established himself as former coach Pep Guardiola's first-choice goalkeeper.
The signing is Leeds' third permanent arrival of the transfer window following the additions of Harry Wilson and Tarik Muharemovic, as manager Daniel Farke continues to strengthen his squad ahead of the new campaign.
Leeds finished 14th in the Premier League last season and will open their new league campaign against Nottingham Forest on 22 August.
Before then, Farke's side continue their pre-season preparations with a home friendly against Bundesliga clubs RB Leipzig at Elland Road on Saturday.
