With extra-time beckoning, Zamora curled a delightful finish into the corner of the net after a series of defensive errors by the Derby defence in the build-up to secure victory for QPR's relieved manager Harry Redknapp and chairman Tony Fernandes.
Promotion is worth at least 80 million pounds for QPR, who return to the top flight after one season in the Championship (second division) along with champions Leicester City and second-placed Burnley who went up automatically.
Following a lacklustre first half, Derby dominated after the break but Steve McClaren's usually free-scoring side were left to rue their failure to get on the scoresheet.
It was the second time Zamora had scored the only goal to clinch victory in a Championship playoff final having struck the winner for West Ham United against Preston North End in 2005.
"I scored the winner for West Ham to get back in the Premier League as well but this was equally important," the well-travelled striker told Sky Sports. "It was a massive game and I'm so pleased for all of the lads.
"To score the winner in the playoffs is a magnificent feeling. I never thought it would have happened again. We've worked hard all year, we really have.
"We've got a great togetherness, after the last playoff game (a 2-1 semi-final victory over Wigan Athletic) we were never going to die, we fight to the end and we did that again today."
CYNICAL CHALLENGE
Torrential rain greeted the players and ensured chances were at a premium with Will Hughes' penalty appeal for Derby the only notable incident in the first period.
The second half was more open and after QPR's 20-goal striker Charlie Austin fired narrowly wide, the Hoops had the experienced O'Neil dismissed for a cynical challenge on Derby forward Johnny Russell as he bore down on goal.
The tone for the rest of the game was set with Derby dominating possession but Redknapp's stubborn side - who had finished one spot and five points behind third-placed Derby in the final league standings - refused to wilt under pressure.
The game looked to be heading for extra time when Zamora took advantage of a poor attempted clearance by defender Richard Keogh inside the area as he kept his cool to clinically steer the ball home from 10 metres to delight the Hoops fans.
QPR will now hope they can follow in the footsteps of the last three teams promoted to the Premier league via the playoffs - Swansea City, West Ham and Crystal Palace - all of whom survived with respectable mid-table finishes.
QPR's debts jumped to 177.1 million pounds for the year to May 2013 from about 91 million in the previous year according to their accounts published in March after they splashed out on players so the promotion windfall will be welcomed by Fernandes.
"The whole club has earned this moment," chairman Fernandes said. "We've been hammered all season and attacked in the press but we never gave up.
"We kept moving with our academy and with our stadium. We've got a good manager despite all that has been said. It's a very good feeling to be going up but the hard work starts here.
"It's true I'm a bit of a richer man today but really it's a secondary emotion. I just wanted to win so badly."
(Reporting By Tom Hayward, editing by Pritha Sarkar and Ken Ferris)
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