Thornton, who defeated Phil Taylor to reach the final, came back from 4-2 and 5-4 down to see off White and claim his eighth PDC Pro Tour title.
“I’m delighted to win this tournament,” said the Scotsman, who continues his Premier League campaign against in Aberdeen on Thursday.
“I’ve felt a bit of luck has gone against me at times this year so for it all to come together and win a title is fantastic.
“I’ve been playing well and this will give me a lot of confidence for the rest of the Premier League and other tournaments this year.”
Thornton began his glory charge with a 6-3 win over David Pallett before 6-1 triumphs over Aden Kirk and Wayne Jones earned him a place in the last 16.
There, he defeated Andy Parsons before claiming a 6-5 success over Richie Burnett in the last eight to set up a semi-final showdown with 16-times World Champion Taylor.
‘The Thorn’ raced into a 3-0 lead against the world number two before seeing his lead cut to 4-3 but, when Taylor missed a dart at the bull to force a deciding leg, the Scot took out 76 to claim a 6-4 victory.
Thornton then finished the job with a 6-5 win over White in the final, which included a fabulous 144 checkout from the former UK Open winner.
Thornton faces Raymond van Barneveld in the Premier League on Thursday.