The 23-year-old was playing for Braintree in the Ryman League when Brighton boss Mark McGhee, plucked him from obscurity in the summer.
Revell spun and shot from the edge of the area to clinch victory for Brighton who were reduced to ten men moments later when Dean Cox, who was booked for jumping into the crowd to celebrate the goal, was dismissed for a foul on Lee Williamson.
Revell almost scored with his first touch when he pounced on Paul Hurst's weak back-pass but Neil Cutler blocked his shot.
Rotherham's summer signing Ritchie Partridge forced a smart save from Wayne Henderson and then Delroy Facey and Partridge combined to set up Williamson who fluffed his shot.
Another Millers debutant Eugen Bopp shot wide on 28 minutes and then the Millers had a lucky escape when Dean Hammond nipped in front of Cutler and headed Cox's cross wide.
Revell opened the score on 44 minutes curling his shot around Cutler after Cox had cushioned Richard Carpenter's crossfield ball into his path.
Both Revell and Cox were booked for jumping into the crowd with Cox sent off just moments later for a foul on Williamson.
Revell continued to show his promise in the second half despite being the lone striker, beating Ian Sharps for pace but dragging his shot across goal.
A clipped cross from Partridge found Williamson but his header forced a comfortable save from Henderson.
Brighton substitute Colin Kazim-Richards burst clear late on but shot into the side-netting.
Rotherham replacement Martin Woods missed the Millers best chance to equalise when he scooped the ball over the crossbar.