The 23-year-old notched his fourth goal of the campaign with just five minutes left on the clock to claim a richly merited triumph for the Ayrshire outfit.
Steve Clarke, fresh from his GMB manager of the year nomination, also saw his Killie side strike the post through Eamonn Brophy, while Jambos goalkeeper Zdenek Zlamal was forced into several sharp stops in the first half.
To compound Hearts' misery, Uche Ikpeazu limped off early in the second half with a suspected hamstring injury and could be a doubt for the Scottish Cup final against Celtic on May 25.
Killie dominated possession in the opening exchanges, swiftly creating the first clear chance. Rory McKenzie surged into the Jambos box and slipped a fine pass to Brophy, who was denied by a superb point-blank save from Zlamal.
Only a magnificent last-ditch challenge from John Souttar denied Killie the lead midway through the first period, with the Scotland defender clearing the ball off the toes of Liam Millar as he was about to tap a McKenzie delivery into a gaping net.
Kilmarnock's Alex Bruce produced a similarly heroic intervention when Ikpeazu capitalised on a defensive mix-up and rounded Daniel Bachmann. However, as the Englishman attempted to roll the ball into an empty net, the 34-year-old was on hand to make the dramatic block.
Brophy, a constant menace leading the line for the visitors, came closest to breaking the deadlock in the first 45 when he met a super Millar delivery, only to see his shot crash off the base of the post.
Hearts were dealt a hammer blow two minutes into the second period when Ikpeazu pulled up with an apparent hamstring issue and had to be replaced by Sean Clare. With the Scottish Cup final just three weeks away, manager Craig Levein will be sweating over the fitness of his attacking focal point.
The Jambos did not wilt without their towering marksman and came close when Steven MacLean nodded a Jake Mulraney delivery towards the corner of the net, but Stephen O'Donnell was in the right place at the right time to hook clear.
However, it was Kilmarnock who claimed all three points with just five minutes on the clock courtesy of Findlay, who latched on to a loose ball after a Youssouf Mulumbu cross was only half-cleared and lashed a magnificent drive beyond Zlamal, sparking wild scenes in the away end.