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.
After producing 113 to level the final at 2-2 in Cheltenham, the world number five won four of the next five frames to leave himself in command before they play to a finish on Sunday evening at 7pm.
Carter could only muster 11 points in three frames as Trump produced knocks of 63 and 54 to establish a 5-2 lead.
Carter halted the bleeding with a knock of 88 in the eighth frame, but Trump finished the session with a sparkling 132 to open up a three-frame advantage.
The first man to 10 frames wins the title and a £100,000 winner's cheque.
WORLD GRAND PRIX RESULTS
FIRST ROUND (best of seven frames)
Monday, February 4
- Ronnie O’Sullivan 2-4 Marco Fu
- Mark Allen 4-2 Gary Wilson
- Barry Hawkins 4-1 Ryan Day
- Stuart Bingham 4-1 Zhao Xintong
Tuesday, February 5
- Martin O’Donnell 3-4 Ali Carter
- Jimmy Robertson 3-4 Mark Davis
- Mark Williams 3-4 Yuan Sijun
- Neil Robertson 3-4 Xiao Guodong
- Joe Perry 3-4 Tom Ford
- Stephen Maguire 4-1 Mark King
- Judd Trump 4-3 Stuart Carrington
- Jack Lisowski 1-4 Ding Junhui
Wednesday, February 6
- Mark Selby 4-1 Shaun Murphy
- John Higgins 2-4 Noppon Saengkham
- David Gilbert 4-0 Yan Bingtao
- Kyren Wilson 4-3 Matthew Stevens
LAST 16 (best of seven frames)
- Xiao Guodong 4-1 Mark Davis
- Tom Ford 2-4 Judd Trump
- Stephen Maguire 2-4 Yuan SiJun
- Barry Hawkins 4-1 Marco Fu
Thursday, February 7
- David Gilbert 4-0 Ding Junhui
- Ali Carter 4-1 Mark Allen
- Kyren Wilson 4-0 Stuart Bingham
- Mark Selby 4-2 Noppon Saengkham
QUARTER-FINALS (best of nine frames)
- Ali Carter 5-1 David Gilbert
- Xiao Guodong 5-4 Yuan Sijun
Friday, February 8
- Mark Selby 1-5 Judd Trump
- Kyren Wilson 2-5 Barry Hawkins
SEMI-FINALS (best of 11 frames)
Ali Carter 6-0 Xiao Guodong
Saturday, February 9
Judd Trump 6-5 Barry Hawins
FINAL (best of 19 frames)
Ali Carter 3-6 Judd Trump
Ali Carter 6-10 Judd Trump