Bent, who is Villa's record signing after joining from Sunderland in January 2011 in a deal reportedly worth up to £24 million, has been limited to seven Premier League appearances from the bench this season.
The 30-year-old - capped 13 times by England - completed a medical at Brighton on Wednesday and will remain with the Amex Stadium outfit until the end of December.
"We are delighted to welcome Darren to the club, and I hope he will score plenty of goals for us during his time with us," said manager Sami Hyypia.
"His record speaks for itself. He is a top-class striker with a more than 100 Premier League goals with Charlton, Spurs, Sunderland and Aston Villa.
"Three years ago he was a regular in the England squad under Fabio Capello; there is no doubting his ability to score goals.
"He also wants to play regular games and that is evident in his willingness to step down from the Premier League to the Championship."
Bent's first match with Brighton will be against Fulham, where he spent last season on loan, on Saturday.
Also dropping down to the Championship is Crystal Palace midfielder Adlene Guedioura, who has joined Watford for a month.
