The 17-year-old came close to scoring a remarkable hat-trick, but instead had to settle for a match-winning brace and the adulation of 40,000 supporters when brought off with 10 minutes to play.
Sunderland had been left to rue the lack of a senior striker in the opening weeks of the campaign, struggling to turn their good play into points. Twenty minutes into this game it felt a familiar tale, the home side enjoying almost 70 per cent of the ball but yet to produce a shot.
When the first effort of the game was registered shortly after, it was the visitors who took the lead.
It was a lovely move to work the ball into the box, where Odoffin was surprisedto find himself free. The forward took one touch and rifled a low effort past Anthony Patterson.
There was relief in the Stadium of Light when it took just a minute for Mowbray's side to respond, the ever-dangerous Jack Clarke cutting inside and standing up a cross to the back post. Dan Neil was there to meet it and Bellingham was able to convert his first senior goal from a matter of yards out.
Sunderland continued to enjoy the better of the contest and took the lead in the second half when Bellingham again was found free in the box, this time curling an effort past Viktor Johansson.
The midfielder came close to landing a remarkable hat-trick when he was found with a cross just moments later, but a strong block allowed Rotherham to stay in the game.
The visitors continued to threaten from set plays even if it was the hosts who were enjoying the better of the play, and substitute Tolaji Bola in particular will feel he could have done better when meeting a delivery into the box.
The scoreline meant the hosts were never comfortable even as substitute Luis Hemir went close with a powerful long-range effort late on, but the Black Cats were ultimately able to see out five minutes of stoppage time to secure a welcome victory.