The 23-year-old Dutchman took the opening leg but it was King who was in imperious form early on in taking the first set by 3-1, and the next by the same scoreline.
Finishes of 102, 120 and an incredible 152 checkout had the Norfolk thrower way ahead at 3-0 and cruising to his own inaugural major televised title.
However the Dutch youngster finally found his best form and double 16 saw him get his first set on the board but he inexplicably missed six darts for the fifth set as King moved 4-1 up and just two sets away from glory.
Van Gerwen, though, won six straight legs to kickstart his challenge again in pulling back to 4-3 before winning the eighth set 3-1 to square the game.
He then came from 2-0 down in set nine to lead the game for the first time, before sealing victory and his maiden major in style by taking the next set 3-0, completing victory with a superb 145 checkout.
"It's the best day of my life," said van Gerwen, who moves up to eighth in the PDC Order of Merit.
"Mervyn was fantastic at the beginning of the game and I couldn't concentrate but he gave me some chances and I started finishing better.
"I'm not a person who gives up so this feels very good for me - I'm so happy to have won."