Gabby Agbonlahor opened the scoring in a confident first-half showing from the host, only for Saido Berahino to score with the Baggies only shot on target before a frantic finale.
Villa was without a Premier League win since Dec. 7, but moved three points clear of the bottom three amid exuberant celebrations from new manager Tim Sherwood on the touchline.
Benteke kept his cool in the 93rd minute, moments after West Brom goalkeeper Ben Foster lost his bearings in tearing from his goal to bring down Matthew Lowton, handing Sherwood his first league win since taking charge.
|VIEW FROM VILLA PARK
|By Tom Davis
A dramatic end to this game was ensured by Ben Foster after the Albion keeper fumbled a shot from Fabian Delph only to foul Matt Lowton on the rebound for a penalty. Christian Benteke stepped up to slot coolly from the spot to secure a valuable win and Villa's first in 13 in the league.
Foster, who was also at fault in the first half but saved himself by clawing Gabriel Agbonlahor’s shot off the line, has cost his side a deserved point on the balance of play in the second.
Tim Sherwood will feel the win is justified though after dominating the first half with two shots off the line and a Delph effort off the post. Villa moves out of the bottom three with Sherwood’s first win in charge – a huge three points.
Nerves set in after Saido Berahino's 66th-minute equalizer, but the Villa players gathered themselves to launch a decisive late rally and boost their club's survival prospects.
Charles N'Zogbia was preferred to Scott Sinclair in the only change to the Villa line-up.
Berahino and Brown Ideye overcame respective foot and knee injuries, giving West Brom head coach Tony Pulis the opportunity to name an unchanged XI.
The forward duo failed to make the most of a fifth-minute opening and then saw little to encourage them during the early stages as Villa pushed its visitor back.
Agbonlahor was almost gifted an opener when Benteke squared for him to shoot and Foster embarrassingly fumbled before grasping the ball on the line.
West Brom backed off too readily for Tom Cleverley to fire over in the 19th minute and then fell behind when Benteke won a flick on from goalkeeper Brad Guzan's clearance and Agbonlahor sped away from Joleon Lescott to slot between Foster's legs.
The Villa attacker's trademark pace and West Brom's surprising weakness against the long ball were on show again in the 28th minute, but Lescott got back to clear from the goalmouth after Agbonlahor poked beyond Foster.
Pulis was left with plenty to ponder at the interval, having gratefully watched Fabian Delph's fierce drive cannon back off the inside of the upright.
Lescott found himself in the referee's notebook for bringing down the rampaging Agbonlahor after 52 minutes, Ashley Westwood sending the resulting free kick over.
West Brom had barely created a chance of note as the hour approached, but should have been level when Craig Dawson escaped the attentions of Jores Okore to head Chris Brunt's free kick wastefully wide at the near post.
But Berahino levelled matters with a smart header after Lescott had turned a corner back into the penalty area with the Baggies first and only shot on target.
Shortly after, substitute Jack Grealish sidefooted weakly at Foster and the England goalkeeper kept out a stinging drive from Delph before switching from hero to villain.
Foster raced out to clatter into Lowton, leaving Benteke to score the winner from the spot as he did in the same fixture last January.