Resuming 6-3 clear from the afternoon session at The Centaur in Cheltenham, Trump was forced to be patient as Carter won three of the first four frames to close to 7-6 behind with breaks of 99 and 83, including a steal on the black to pinch the 13th frame.
But the interval came at the wrong time for Carter, who could not maintain his revival with world number five Trump largely dominant in seeing out the final three frames as runs of 71, 78 and 54 saw the Bristol player over the winning line.
Trump collects a winner's cheque for £100,000 after claiming the 10th ranking title of his career at the age of 29 with Carter earning £40,000 for his run to the final.
"It was so hard today - I think Ali's safety play is far superior to what I've faced recently," said Trump. "Even tonight from 6-3, he still had a chance to go 7-7 and I didn't really do much wrong. Proud of the way I held myself together.
"It's nice to see Ali back in a final. I knew it was going to be a tough game. The crowd this week have been superb and I'm very happy to play here."
He adds the World Grand Prix to titles claimed at the Northern Ireland Open and The Masters in recent months as he prepares to head for the Welsh Open in Cardiff and a first-round match with Harvey Chandler on Monday evening.
Carter meets 2015 world champion Stuart Bingham on Tuesday in one of the stand-out matches of the first round at the Welsh Open.
FIRST SESSION REPORT
Judd Trump needs four more frames to win his third title in four months after opening up a 6-3 lead over Ali Carter in the World Grand Prix final.
Having edged out Barry Hawkins 6-5 in a final-frame decider in the semi-finals on Saturday night, Trump - winner of the Northern Ireland Open and The Masters in recent months - set about showing his revitalised all-round game against his fellow former World Championship finalist.