USA international Tyler Adams was reunited with Leeds manager Jesse Marsch after completing a reported £20 million ($24 million) move from RB Leipzig on Wednesday.
Adams previously played under his compatriot at both New York Red Bulls and Leipzig.
The 23-year-old is expected to fill the role vacated by Kalvin Phillips following his move to Manchester City.
"I am super excited," Adams told LUTV. "Talking to my friends who have played in the Premier League, they say it's one of the best atmospheres they have ever played in.
"Now to have those fans supporting me, it's going to be something special."
Adams made his Major League Soccer debut as a teenager under Marsch in 2016 before moving to Europe three years later with Leipzig, where the Leeds boss was assistant to Ralf Rangnick before taking on the senior role.
He made 101 appearances for Leipzig, most memorably scoring the winner in the Champions League quarter-final victory over Atletico Madrid in 2020.
He joins his international teammate Brenden Aaronson, who joined last month from another of Marsch's former clubs Red Bull Salzburg.
Leeds have also signed Darko Gyabi, Rasmus Kristensen and Marc Roca as they look to avoid another Premier League relegation battle after narrowly avoiding the drop last season.