Villa are splashing out an initial £18million for Bent but additional add-ons mean the final figure could rise by another £6million. The England player is in line to make his debut in Saturday evening's home Barclays Premier League clash with Manchester City.
Bent said: "Aston Villa is a massive football club and as soon as I knew they were interested in signing me I wanted to join. The size of the football club and the history of the club are major reasons for me coming here."
He added: "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."