Sinner's third title of the season means he will move to a career-high second in the ATP world rankings on Monday ahead of Spain's Carlos Alcaraz.
Sinner finished the hard court season in electric form, having won 25 of his last 26 matches -- the only defeat coming to Alcaraz in the semi-final of Indian Wells.
The Italian took care of business in 72 minutes and never looked in danger after he broke in the fifth game of the first set, facing just one break point in the entire match.
"As this tournament went on, I felt better and better. Today's performance was really good. I'm just proud of how I handled the situation," Sinner said.
Sinner clinched the first set with his second break, a brilliant backhand down the line that brought spectators to their feet.
Dimitrov, with his trademark one-handed backhand strokes and willingness to go to the net, was enjoying plenty of support from the home crowd but Sinner's ice-cool approach and pristine technique was too much for him.
The Italian broke in the second set to go 3-1 up and with his serve strong and returns rock solid, it was a procession to victory from that point on.
Sinner added the Miami title to his crowns this year at the Australian Open and the Rotterdam Indoors.
His title came in his third appearance in a Miami final -- he lost to Poland's Hubert Hurkacz in 2021 and Daniil Medvedev last year.
Sinner's previous Masters 1000 title came in Toronto in 2023.
Dimitrov will return to the top 10 in Monday's rankings for the first time since October 2018. His run to the Miami final included a quarter-final win over Alcaraz and a semi-final victory over world number five Alexander Zverev.
