Czech Kvitova, appearing in her first Miami final, triumphed 7-6 (16/14) 6-2 at Hard Rock Stadium, a victory which will return the veteran to the top 10 in the world rankings.
Rybakina came into Miami after winning the title at Indian Wells and was looking for the rare 'Sunshine Double' of both WTA Masters events.
It was a tight, serve-dominated battle until Kvitova broke to go 5-4 up but Rybakina, who represents Kazakhstan, immediately broke back.
The tie-break was a 22-minute, 28-second long, 30-point shoot-out which two-time Wimbledon Kvitova emerged triumphant from when Rybakina returned to the net.
Kvitova took that momentum into the second set, breaking early to go 2-0 up and from then on she never looked like letting her opponent, 11 years her junior, back into the contest.
Rybakina couldn't convert a breakpoint in the next game and then she herself was broken again when serving to stay in the match at 5-2 down.
Kvitova, who has now won 30 of 41 career finals, said the tie-break had turned the contest in her direction.
"I'm still surprised. I think the tie-break really decided the whole match in the end...it was probably the longest in my career and somehow I managed it," she said.
"(She hit) so many aces at the beginning of the tie-break, I was like oh my God, I couldn't even play, so it was a little difficult," added Kvitova, who now has nine WTA 1000 titles.
"I had to slowly serve it out very well today and I am glad I made it in the end but to be honest I have no idea how I did it," she added.
Kvitova won 78 percent of her service points (52 of 67) and finished with 29 winners to 14 unforced errors
Rybakina fired 12 aces in the match and became the first player since Serena Williams at 2016 Wimbledon to hit 10 or more aces in six consecutive matches in a single tournament.
