The 32-year-old claimed 4/56 from 10 overs, before smacking 150 not out from 143 balls as Kent chased down Glamorgan's total of 274 with 11 balls to spare.
Meanwhile, Billings' Chennai Super Kings were crowned IPL Champions after defeating Brathwaite's Sunrisers Hyderabad by eight wickets in the final on Sunday night.
Kent Spitfires win by 4 wickets!— Kent Cricket 🏏 (@kentcricket) May 25, 2018
Joe Denly ends with a career-best one-day club record innings of 150*. 19 fours and 2 sixes with the bat after 4/56 with the ball.
Scorecard & highlights: https://t.co/AggahCDImu pic.twitter.com/sP4RyVLDJv
Despite playing an important role for Chennai throughout the tournament, Billings did not suit up in the final, while Sixers teammate Brathwaite scored 21 off 11 balls and finished with bowling figures of 1/27.