The hard-serving 21-year-old from Thornhill, Ont., won the Chennai Open, defeating top-seeded Janko Tipsarevic of Spain, 6-7 (4), 7-6 (4), 7-6 (4).
The fourth-seeded Raonic, who beat Nicolas Almagro of Spain in the semifinals, hit 35 aces in a marathon match that lasted three hours 16 minutes.
The Canadian is 2-1 in ATP World Tour finals, claiming his first title in San Jose last February. He followed that up by finishing runner-up to Andy Roddick in Memphis a week later.
Raonic rose from No. 156 in the rankings to a career-high 25th last season before moving down slightly to his current No. 31. He won the ATP Newcomer of the Year award last year.