The England star, who had already scored on his first LaLiga and Champions League appearances from the club, hammered a strike into the top corner from 25 yards in the second-half as he produced a moment of magic out of nothing.
Real needed it too, as they struggled to find a way back into the match. Ilkay Gundogan had put Barcelona in front inside six minutes, and it was a lead they deservedly maintained until Bellingham's intervention midway through the second-half.
Vinicius Jr cut an increasingly frustrated figure, having a heated discussion with Barcelona manager Xavi as he appeals for a free-kick continued to be waved away, and the Brazilian's mood was not improved when Ferran Torres rugby-tackled him into the technical area to stop a Real counter.
The visitors did not particularly improve immediately after the break, with Barcelona close to doubling their lead. Fermin Lopez had hit the woodwork in the first-half and Inigo Martinez did likewise with a header shortly after the break, Kepa Arrizabalaga then forced into action to deny Ronald Araujo with the rebound.
It looked as though the story would be Bellingham dragging Real to a Clasico point, as he rifled home a stunning equaliser midway through the second period, but it got even better. The ball fell for him in the box in the second minute of added-time and he made no mistake to continue his remarkable start to life in Spain, making it 13 goals in as many appearances this season.
The result lifts Real back to the top of LaLiga, ahead of Girona on goal difference, with Carlo Ancelotti's side now four points ahead of Barcelona.