Though the Academy graduate has been in and around the first team for the past couple of seasons, the move to The Hawthorns will give the 20-year-old valuable game-time at the Championship club.
Adarabioyo has made eight senior appearances for the Blues and has been connected with the Club since he was five.
The Manchester-born centre-half made his debut against Chelsea in 2016 and in 2016/17, played against Steaua Bucharest and Celtic in the Champions League and Swansea in the Capital One Cup.
Last season, Tosin played against Leicester and Wolves in the Carabao Cup and Shakhtar Donetsk and FC Basel in the Champions League.
He has also represented England at youth level on 15 occasions.
Keep a close on Tosin’s progress in our Loan Watch feature throughout the season.