The 24-year-old underwent a medical on Wednesday afternoon before agreeing to join the Championship club.
Bennett has spent the past two years with Villa following a move from Middlesbrough.
"I'm delighted we have agreed with Joe and Aston Villa to bring him here on a season-long loan," Brighton boss Sami Hyypia told the club's official website.
"He is a dynamic left-back, who's very comfortable on the ball. He's very mobile and will suit the way we want to play. He is a good footballer, who knows how to use the ball and I hope he will be a very good player for us."
Bennett could make his debut for Brighton on Saturday when they host Bolton Wanderers in the Championship.