The 21-year-old centre-back will spend the 2026/27 Championship campaign at Turf Moor after gaining valuable experience with Watford last season.
"I'm super excited, I can't wait to get going. I had my first training session today and I've really enjoyed it so far, meeting the manager and my teammates,” said Alleyne.
"I first heard of the interest a couple of months ago now, and I'm so glad it got done. It's a huge team, a Premier League team to be honest, and I'm so buzzing to be here."
Born in Bristol, Alleyne began his career in Southampton’s academy before joining Manchester City in 2021. He quickly progressed through the club’s youth system and signed his first professional contract a year later.
The defender was a regular for City’s U21s while also earning exposure to the first team, featuring in a Champions League squad against Red Star Belgrade in 2023 before being named in a Premier League squad against Everton the following year.
Alleyne joined Watford on loan last summer, making 17 appearances before returning to City in January.