Bent has signed in time to be eligible to play in Fulham's opening Barclays Premier League game of the season at former club Sunderland.
The striker was Villa's record signing when he arrived from Sunderland in January 2011 but slipped behind Christian Benteke in the pecking order at Villa Park last season.
The 29-year-old will be reunited with Martin Jol, who signed the England international from Charlton Athletic in 2007 whilst manager of Tottenham Hotspur.
Jol told the club's website: "Darren Bent is a striker I have always admired.
"He has shown in the Barclays Premier League that he is composed and clinical in front of goal but, even if he is not scoring, he is involved in some good link-up play, creating opportunities for his team-mates.
"I'm delighted that he has joined us, he gives us pace up front and I am confident that he will add to our goals scored tally this season."
Bent has scored over 100 Premier League goals since 2005, playing for Charlton, Tottenham, Sunderland and Villa as well as four goals in 13 appearances for England.