The Japanese world number 44 beat the Russian twentieth seed 6-3 6-2 out of one hour 10 minutes.
Osaka, who dropped only one set all through the competition, overwhelmed on serve to outmuscle Kasatkina.
The 20-year-old is the most youthful champion at Indian Wells since Ana Ivanovic in 2008.
It was the first run through two players matured under 21 had challenged the last at Indian Wells since Serena Williams, at that point matured 20, beat 18-year-old Kim Clijsters in 2001.
Osaka, Williams, and Clijsters are the main unseeded players to win the ladies' title at the occasion
The two players had removed a few best-positioned players in California, prominently in the semi-finals where Osaka whipped world number one Simona Halep and Kasatkina outlived Venus Williams in three sets.
Kasatkina softened up the opening session of the match after progressive forehand mistakes from Osaka, yet a fine forehand champ in the following diversion set the match back on serve.
An ace from Osaka in the seventh diversion spared breakpoint and the Japanese got the definitive break in the following amusement.
A strike - her fourteenth champ, contrasted and only three from Kasatkina - enabled Osaka to take the main set in 39 minutes.
Osaka proceeded with her predominance, softening up the opening round of the second set before dashing to a 5-1 lead with a forehand down the line.
Kasatkina discovered her strike to drive her rival to serve out the match yet Osaka hit the quickest serve of the match - a 118mph expert - on her approach to finishing off a triumph.
The win is Osaka's first title at any level of tennis and will see her turn up to a vocation high of 22nd on the planet rankings.