"The fee starts at £18m, rising with add-ons to £24m," explained BBC Radio 5 live reporter Pat Murphy.
The England player could make his debut in Saturday Premier League clash with Manchester City at Villa Park.
His shock move to the Midlands outfit smashes Villa's previous transfer record when they paid £12m for James Milner from Newcastle in August 2008, a fee matched the following year when Stewart Downing joined from Middlesbrough.
Bent had joined the Black Cats for an initial £10m from Tottenham in August 2009 when he signed a four-year deal with the north-east club.
PHIL MCNULTY'S BLOG Goals come with an expensive tag - and there have never been any shortage of takers willing to pay the price for Bent The London-born star, who began his professional career at Ipswich and also played for Charlton, said: "Aston Villa is a massive football club.
"As soon as I knew they were interested in signing me I wanted to join. The size of the club and its history are major reasons for me coming here.
"There are some top, top players here too, real quality, and I've been able to speak to the manager and the owner about their ambitions for the club. I'm very excited about being a part of what we hope to achieve."
However, Sunderland boss Steve Bruce was not happy to be losing the England striker.
He said: "It's hugely disappointing that Darren has decided that his future lies away from Sunderland and the players, our supporters and the club as a whole have every right to feel massively let down.
"The timing is especially hard to take, given that we are progressing positively and are in a great position to push on.
"Everyone has been nothing but supportive of Darren in his time at Sunderland but it's obvious he's not been himself in training and we've certainly not seen the best of him in games in recent weeks - and we now understand why.
"I've always stated that my aim is to build a talented, young squad for the long-term to help the club achieve sustained success and I want Sunderland fans to know that our ambitions haven't changed on that front."
DARREN BENT'S CLUB HISTORY Ipswich: 1.08.2001 (trainee)joins Charlton: 1.06.2005 (for a fee of £2.5m)joins Tottenham: 29.06.07 (£16.5m)joins Sunderland: 5.08.2009 (£10m, plus add-ons)joins Aston Villa: 18.01.11 (£18m, plus add-ons) Black Cats chairman Niall Quinn added: "Darren has now left the club and it's important we move on quickly.
"We've worked hard in the last 36 hours to get what we feel is a fair price for him. Of course it presents us with significant challenges from a football perspective which we didn't envisage, but we'll deal with it and are working hard to find a solution both in the short-term and more importantly the longer term."
Bent's signing is also a show of faith in manager Gerard Houllier by Villa's American owner Randy Lerner, despite the Frenchman struggling to steer the club away from the relegation zone since taking over in September.
The forward's switch from a club currently sixth in the Premier League to one fourth from bottom of the top flight leaves Bruce with a big void to fill.
Bent, who started his career at Ipswich before spells at Charlton and Spurs, scored 25 times last season and has notched 11 goals so far in the current campaign.
Bruce has fellow strikers Asamoah Gyan and on-loan Danny Welbeck, who is currently injured, to call on and, although they have eased the reliance on Bent with 14 goals between them this season, they will have to prove they have the consistency to ease the impact of the imminent departure.
Bent has one of the best strike rates during recent seasons in the Premier League.
Since 2005, he has scored 81 league goals, with only Manchester United's Wayne Rooney and Chelsea forward Didier Drogba ahead of him in the scoring charts, with 82.
Although he missed out on selection for the 2010 World Cup last summer, Bent did grab his first international goal in September when he scored after coming on as a substitute in a 3-1 win over Switzerland.