Warren hit five birdies in a final round of 68 for a total of 275 and nine under.
He was pushed all the way by Dredge, who went round in 70 for seven under overall while England's Phillip Archer was third, five shots off Warren.
"I felt the last couple of years I’ve been close to winning a couple of times but for whatever reason it hasn’t quite happened for me, whether I’ve made mistakes or someone else has played really well," said Warren.
“This summer I feel more confident than I’ve ever done. Today I kept telling myself I was swinging the club really well and I was confident in what I was doing.”
Dredge, the halfway leader, was left looking for his first title in six years.
“In a way there are mixed feelings in that if someone said they’d give me second at the beginning of the week it is a great result, considering I’ve not had a chance to win in a long time. But it was a chance to win a tournament,” he said.
“Marc did play really well and I didn’t play well enough, but it would have been nice to have pushed him a little harder coming down the last few.”