Sharp struck as this South Yorkshire derby looked set to end in a snow covered Oakwell stalemate.
It sent FA Cup semi-finalists Barnsley to only their third home defeat of the season, but they now have only one win in their last eight league outings.
James Beattie flicked on a long ball and lifelong Blade Sharp charged to the edge of the area and crashed his angled shot past Luke Steele.
Cup hero Steele denied top scorer Beattie two minutes later when he latched on to a Sharp cross eight yards out.
It was another heart-warming display for United fans as Kevin Blackwell's side continued their impressive revival.
United finished stronger and just before the killer blow veteran midfielder Gary Speed went close when he burst through 15 minutes from the end, but smashed his shot against the upright.
Barnsley were denied a first-half lead when Paddy Kenny pulled off a superb full-stretch save to turn round a blistering 25-yard effort from Diego Leon.
And the home side were fuming when they missed out on a penalty, when referee Lee Probert dismissed strong claims after Stephen Foster was dragged back in the area as he darted in to meet a Brian Howard cross.
Striker Kayode Odejayi, scorer of Barnsley's FA Cup quarter-final winner over Chelsea, missed a glorious chance when he headed over.
Martin Devaney should have done better when he hit a shot on the turn but lifted it over Kenny's goal.
And with 15-goal leading scorer Beattie watching from the bench, striker Rob Hulse blew United's best early effort when he headed David Cotterfill's cross wide.
Barnsley had another penalty claim dismissed when Odejayi appeared to be dragged down in the area by Chris Morgan.