The 24-year-old left-back moves on a month's loan and goes straight into the squad for Saturday's game at Sixfields against Burton Albion.
"You don't sign for a club like Villa unless you've got something about you," Town manager Chris Wilder told BBC Radio Northampton after snapping up the Irishman.
Stevens moved to Villa Park in early 2012 after a deal had earlier been agreed with Shamrock Rovers for whom he impressed both in the League of Ireland and European competition.
Villa manager at that time, Alex McLeish said of his new signing: "He's a young prospect, a boy with bags of potential."
Stevens has made 9 appearances for the Premier League club since then and played on loan at both Notts County and Doncaster Rovers last season.