The former Aston Villa midfielder had scored just 19 goals in six years before this season but took his tally to 22 for this campaign with the second goal in stoppage time at the end of the first half.
Ross McCormack had earlier opened the scoring as the Foxes were condemned to a third defeat in a row, despite Steve Howard's strike early in the second half.
Cardiff had centre-half Gabor Gyepes sent off with 19 minutes left but held on to cement fourth place in the table.
The home side settled quicker in a scrappy start and took the lead in their first attack of any substance in the 10th minute.
Stephen McPhail and Chris Burke combined well to move the ball into the area where on-loan Manchester City forward Kelvin Etuhu arrived to smash in a low shot on goal.
Leicester goalkeeper Chris Weale reacted well to get a strong hand on the shot but the ball squirmed loose for McCormack to slot in with his left foot.
It was the Scotland international's fifth goal of a quiet season and gave the Bluebirds the ideal footing.
Winger Burke drilled a shot wide from 20 yards as Dave Jones' side looked to kill off a Leicester side which looked low in confidence, before defender Darcy Blake hobbled off to be replaced by Adam Matthews.
Matthews was into the action before half-time as he hooked a shot over the bar and it was no surprise when Whittingham doubled the lead in the final seconds of the half.
Another slick passing move saw the Bluebirds carve Leicester open, and when Gavin Rae popped up in the area he was able to square for Whittingham to convert.
Leicester boss Nigel Pearson introduced targetman Howard at the break and he took just seven minutes to find a way back into the game.
Martyn Waghorn delivered a vicious corner with his left foot and when goalkeeper David Marshall made a hash of clearing the ball with a punch, Howard was able to smash in a left-footed volley from 12 yards.
Waghorn was then replaced by on-loan Everton striker James Vaughan and within two minutes his pace led to the red card for Gyepes.
Nolberto Solano slid a pass down the side of the Cardiff defence and Vaughan had his heels clipped by Gyepes as he looked to run in on goal to leave referee Fred Graham with no option but to produce the red card.
Richie Wellens forced Marshall into a sprawling save as the Foxes pushed for a late equaliser but Cardiff held on for three vital points.