The Czech, who is 10 years older than her opponent, kept her nerve in the game's biggest moments to claim her 30th career title and ninth WTA 1000 crown.
"Experience today played a good role in my mind," Kvitova told reporters after the match.
"I played so many finals. I know I can play well in the final no matter who I'm facing. Mentally it was very important for me to know that."
The former world number two, who had contemplated retirement last year, said her two weeks in Miami as well as her run to the quarter-finals of Indian Wells had left her "really happy and very exhausted."
The loss snapped Indian Wells champion Rybakina 13-match win streak and ended her hopes of claiming the "Sunshine Double" by winning both hardcourt events.
"This means a lot," Kvitova said.
"The young ones are coming up all the time. It's tough to face them all. It's very tiring," she said with a smile.
With the win, Kvitova became the second-oldest woman to triumph at the Miami Open, after Serena Williams in 2015. She will now return to the top 10 for the first time since September 2021.
The twice Wimbledon champion made headlines after her semi-final when she said that she opposed Wimbledon's decision to lift its ban on Russian and Belarusian players amid Moscow's ongoing invasion of Ukraine.
"I'm really appreciating that Wimbledon didn't take them last year," she said on Friday.
Wimbledon organizers said it was an "incredibly difficult decision" and that they "condemn totally Russia's illegal invasion." Russia calls its actions in Ukraine a "special military operation."
Kvitova said athletes from those countries should also not be allowed to compete at the Paris Olympics.
The International Olympic Committee has not yet announced its policy for the Games.
However, Rybakina said the grasscourt Grand Slam had taken the correct decision to reverse its ban on Russian and Belarusian players and allow them to compete at this year's tournament as "neutral" athletes.
Russian-born Rybakina, who switched allegiance to Kazakhstan in 2018, claimed the Wimbledon title last year but missed out on 2,000 ranking points as a result of the men's ATP and women's WTA penalising the Grand Slam for its ban.
She said that she had no problem with Russian and Belarusian players competing without their national flags.
"They have been playing like this for all the tournaments, so it (Wimbledon) was only Grand Slam they were not allowed," Rybakina told reporters.
"So I think that's the way that they are playing, without any flags. I think it's the right decision, I guess."
Players will be prohibited from expressing support for the invasion and must not receive funding from Russian or Belarusian states, Wimbledon organisers added.
