Buttler hammered 131 in 64 balls and captain Brook made 95 not out in 45 deliveries to propel England to 3-257, their third-highest T20 total and highest against India.
"We've managed to get ourselves to No.1 in the world, which was the aim after the second game," player-of-the-series Brook said after his side restricted India to 8-201-8 in reply on Saturday (Sunday AEST).
It rained sixes at the Rose Bowl as Brook and Buttler shared a memorable second-wicket stand of 233, England's highest for any wicket in a T20.
India, who opted to rest 15-year-old batter Vaibhav Sooryavanshi after the teenage sensation failed to make an impact in the three previous games, were made to pay for deciding to bowl first after winning the toss.
Buttler made a welcome return to form by smashing eight sixes and 12 fours as he charged to his second T20 international century.
Brook continued his excellent series, which began with the opening match being abandoned due to bad weather, by clubbing eight sixes and four fours.
Shivam Dube took two late wickets, including Buttler's, but his solitary over cost 22 runs.
"It's been a little bit of a lean patch for a while," Buttler said. "It was a great day for me personally and a great day for the team. I am really happy to get back to my best and contribute to a brilliant series win."
India, displaced by England at the top of the rankings, had a mountain to climb to reach their target and made a poor start when opener Abhishek Sharma was removed for three.
Ishan Kishan struck a 35-ball 56 while Tilak Varma raced to 53 in 25 deliveries but India were always behind the run-rate. Allrounder Sam Curran took 3-36 and leg-spinner Adil Rashid picked up 2-24.
"There's a lot to take from this series," India captain Shreyas Iyer said. "The conditions, the awareness, the adaptations to the wicket.
"Of all the grounds we played on, this was probably the best. The approach to our batting was different today."
The two teams begin a three-match series of one-day internationals in Birmingham on Tuesday.
