Kaboul, a former Black Cats transfer target, scrambled the ball home after Jamie O'Hara's corner had caused chaos in the home side's six-yard box.
Frederic Piquionne stabbed the ball back across the area, and while Nyron Nosworthy attempted to make a last-ditch challenge, Kaboul was on hand to stab the ball home.
The dramatic late strike deprived Sunderland of a sixth home win of the campaign, and cancelled out Darren Bent's tenth goal of the season.
Bent has proved prolific since joining Sunderland in a £10m move from Spurs, and the striker moved into double figures for the season in the 23rd minute.
Jordan Henderson was the provider, nutmegging Marc Wilson before crossing from the right, and after Andy Reid headed the ball back across goal, Bent hooked in a firm finish from eight yards.
With Sunderland passing the ball around crisply in midfield, Henderson almost added a second five minutes later when he curled narrowly past the left-hand post following a pull back from Nyron Nosworthy.
Portsmouth's only first-half effort was a long-range Jamie O'Hara shot that failed to trouble Marton Fulop, but the Spurs loanee asked more questions of the Sunderland shot-stopper at the start of the second half with a curled free-kick from 20 yards.
The Black Cats failed to find much rhythm in the second half, but Reid came within inches of doubling their lead with a 25-yard free-kick that hit the top of the crossbar. However, there was a late sting in the tail, with Kaboul levelling before being dismissed for a second yellow card for removing his shirt in celebration.
SUNDERLAND (4-4-2): Fulop; Nosworthy, Da Silva, Turner, McCartney; Campbell, Cana, Henderson, Reid; Jones (Murphy 85), Bent (Malbranque 90).
Subs: Carson (gk), Anderson, Meyler, Malbranque.
PORTSMOUTH (4-5-1): James; Ben Haim, Wilson, Kaboul, Hreidarsson; Yebda (Webber 77), Brown (Diop 83), O'Hara, Hughes, Dindane; Kanu (Piquionne 62).
Subs (not used): Begovic (gk), Belladj, Finnan, Mokoena.