The Chelsea loanee scored his first goal since October when he headed home from a Jack Grealish cross to break the deadlock.
Villa went into the game with just one win in their last five games, including twice letting the lead slip in a disappointing 3-2 defeat at Burnley in midweek, but scored the decisive goal just before half-time at St Mary’s.
Southampton had two significant VAR decisions go against them, a penalty shout inside the opening period and a stoppage-time offside decision against Danny Ings.
The result sees Villa climb to eighth place, ahead of Arsenal and Chelsea, who have both played more games than the midlands club, while Southampton remain in 11th.
In the 10th minute, Southampton had a penalty shout after a clever heel flick over the defender’s head from Ings, before the striker pulled the ball back to Stuart Armstrong who had his shot blocked by Matty Cash.
The ball appeared to strike the hand of the Aston Villa defender, and VAR referee Mike Dean took a lengthy look at Cash’s outstretched arm which seemed slightly away from his body, before deciding it was not a penalty.
The official line from VAR was that the ball flicked off the defender’s thigh and onto his hand and was not deemed to be a penalty.
Ryan Bertrand, who had missed his side’s 3-1 defeat to Arsenal in the Premier League midweek through suspension, had one of the home side’s better chances of the opening 45 minutes, but his well-struck effort was just wide, finding the side netting.
Aston Villa grew into the game towards the end of the first half and found the breakthrough four minutes from the break. Grealish cleverly picked out Barkley with a first-time cross and the 27-year-old headed past the goalkeeper from close range.
It was Barkley’s fourth goal of the season in all competitions and his first since his side’s 1-0 win over Leeds on October 18.
Southampton went into the game having struggled to score goals in recent weeks, notching just four goals in their last seven Premier League matches, a run which included stalemates against Fulham and West Ham.
Their recent struggles in the final third showed in the first half when they had eight shots, none of which were on target, with Emi Martinez not called upon to make any saves.
After coming on to replace the injured Theo Walcott, Che Adams had an opportunity to level the game for his side. His first shot was saved by Martinez only for a last-ditch tackle from the Villa defence to stop his follow-up effort from finding the back of the net.
In added time, Ings looked to have struck the leveller for Ralph Hasenhuttl’s men, but the forward was flagged offside. A VAR review ruled the striker’s shoulder marginally offside and the on-field decision was upheld.
Despite an impressive start to the season, Southampton have now lost their last three Premier League games.