It was the first points that the Cumbrians had dropped at home since early September and brought to an end their 14 match unbeaten run.
Luke Chambers powered home a header with 14 minutes remaining and in a frantic finish sub Garath McCleary sealed the win from close range.
Forest, who started with three frontmen, rarely threatened in the first half, although Chambers went close when his third minute header was blocked on the line.
Danny Graham should have scored for Carlisle when Chris Lumsdon lifted a brilliant 60-yard pass over the wrong-footed Wes Morgan, but left with just keeper Paul Smith to beat, Graham scuffed his shot wide.
Graham did hit the target in first-half injury-time when he slid onto Simon Hackney's near-post cross, but the 15-goal striker could only poke his shot against Smith from point blank range.
Julian Bennett almost put through his own net after Hackney's driven cross early in the second half, but chances were few for either side.
A lucky bounce fell kindly for Graham on 56 minutes and he unleashed a blockbusting effort from 30 yards that Smith did well to parry.
Home keeper Keiren Westwood was at fault seven minutes later when his hesitancy allowed McCleary to get ahead of him, but the winger's header dropped just wide.
But Westwood was beaten on 76 minutes when Chambers rose unmarked to thunder in a header from Lewis McGugan's free-kick.
Carlisle pushed forward in search of an equaliser and captain Danny Livesey almost netted on 89 minutes only to see his header hit the bar, before McCleary snapped up a rebound with seconds left to seal the win.