Williams' second win at Roland Garros comes 11 years after her first and gives her at least two wins in every Grand Slam event. It comes 12 months after Williams was a very surprising upset victim in the first round of the 2012 French Open.
Since then, Williams is 68-3 with 11 tournament titles and has returned to the world No. 1 ranking.
Saturday's win was the 31st consecutive match win for Williams, a career best.
She holds the championships at Wimbledon and the U.S. Open in addition to the French Open. All told she has 16 major tournament titles.
"Actually 11 years ago I didn't even think I'd still be playing. I never thought I would play past 28, or something like that but I'm still here," William said after the match. "And this one was so good. It's the only one I hadn't won more than one of. Now I have multiple titles at every major, singles and doubles, so I'm really pumped."
Williams improved to 14-2 in matches against Sharapova. They have played four times this year, with Williams winning in the semifinals at Doha and in championship matches in Miami, Madrid and Paris.
Sharapova, the world No. 2, who was seeking to repeat at the championship where she completed her career Grand Slam last year, jumped out to a 2-0 lead but Williams answered by winning four straight games. Sharapova evened the set with a break to 4-4 but Williams quickly broke back and held serve for the first set.
Sharapova fought off five first-game break points but lost the first Williams had in the third game. Williams didn't give Sharapova a chance after that, dropping just two points on serve the rest of the way.
Williams pounded out 10 aces -- three in the final game -- and had 33 winners against 19 unforced errors. Sharapova only had two break chances, which she won both of, but Williams ended up winning more than 75 percent of the points on serve.
Williams completed a French Open in which she lost one set, that coming in the quarterfinals to Svetlana Kuznetsova. Sharapova was the only player to have two sets with at least four games won against Williams.