Bulgarian Dimitrov, who is number 11 in the world, broke once in each set to defeat his 22-year-old Australian opponent – the youngest Cincinnati finalist since Novak Djokovic in 2009.
Kyrgios, who was also aiming to claim his maiden Masters 1000 triumph, hit 31 unforced errors during the contest.
The biggest victory of Dimitrov’s career comes ahead of the US Open, which begins a week today in New York City.
“In the big picture, it means a lot to me,” said Dimitrov, who made it through the entire tournament without dropping a single set.
“I am confident after that, this is what I have been practising for. I am going to enjoy it for a day or two but then it is back to the routine and I will prepare for the US Open.”
In the final of the women’s tournament in Cincinnati, Wimbledon holder Garbine Muguruza comfortably saw off Simona Halep 6-1 6-0.