Academy graduate Targett featured 21 times for Southampton last season, and made 63 appearances overall for the club since making his senior debut five years ago.
"We're very pleased to have Matt join us. He's a player we have been looking at for a considerable amount of time," Villa manager Dean Smith told the club website https://www.avfc.co.uk/News/2019/07/01/transfer-news-targett-arrives.
"He fits our criteria of being a young player with experience of playing in the Premier League and having the potential to develop further.
"He will help make us a stronger defensive unit and we are all looking forward to working with him."
Dean Smith's side have signed Spanish winger Jota and Dutchman Anwar El Ghazi, defender Kortney Hause and Brazilian striker Wesley after their Championship playoff final win over Derby County in May.
Villa, back in the top flight after a three-season absence, kick off their Premier League campaign against Tottenham Hotspur on Aug. 10.
(Reporting by Hardik Vyas in Bengaluru, editing by Ed Osmond)
