Nineteen-year-old Colwill has been at Chelsea for 10 years, having joined the Blues' Academy at Under-9s level. He trained with Thomas Tuchel's squad during pre-season and has featured regularly for our Academy sides, as well as representing England at various youth levels.
The defender now has the chance of top-flight experience with the Seagulls who finished ninth last season.
Colwill spent last season on loan with Huddersfield Town in the Championship, playing 32 games in all competitions and helping them to reach the play-off final, where they were beaten by Nottingham Forest.
“I am really looking forward to working with him on the training pitch, and in matches over the course of the season.
“He plays mostly at centre-back, but has also played on the left as a full-back, and he is a player who is comfortable on the ball."