The world number one and the second seed will meet Saturday after coming through their semi-finals in very different manners.
Williams thrashed Italy's Sara Errani 6-0 6-1 to reach her first Roland Garros final since she won the tournament back in 2002.
Sharapova had earlier coped with a rash of double faults to beat Victoria Azarenka 6-1 2-6 6-4.
"To come back as the defending champion, it's extremely special to get back on that stage where it comes down to the last two players of the tournament," said the Russian.
Sharapova prevailed in a semi-final that swung wildly in momentum, dropping serve in the opening game with a double fault and sealing victory with an ace more than two hours later.
In between, the ferocity and depth of Sharapova's hitting, particularly off the return, was often too much for Azarenka, and 14 winners flew past the Belarusian as the first set raced by.
Azarenka managed to get a foothold at the start of the second, and a brilliant forehand winner off a high-bouncing Sharapova shot set her up to break for 4-2.
With rain starting to fall, Azarenka broke once again to level the match before play was suspended, and when the action resumed a little over half an hour later it was Sharapova who pressed first.
A cross-court winner gave her the break at 2-1 but the double faults that have plagued her in recent years began to tell.
Her ninth, to none from Azarenka, gifted the advantage straight back in game four, and after blasting her way to a 5-2 lead as her returns continued to pepper the baseline, Sharapova faltered dramatically when serving for the match.
Four match points came and went before she lost the game, inevitably, with her 11th double fault of the day.
Azarenka might have thought she had put the pressure on with a quick hold to trail 5-4, but the unpredictable Sharapova serve then clicked and she sealed victory at the second attempt with ace number 12.
"Despite having those match points and not taking advantage of them, I was happy with the way I came out at 5-4 and served it out," said Sharapova.
Williams could not have won in more contrasting, or convincing, style.
Errani might have been last year's runner-up but Agnieszka Radwanska is the only top-five player she has ever beaten, and she was overwhelmed by Williams.
The American broke to love in the opening game and fired 19 winners, dropping just two points on serve, as she won the opening set in 21 minutes.
Williams took the winners count to 26 by swatting away a forehand return to break in the second, and Errani could not get a racquet near a 199km-per-hour ace that flew by her for 3-0.
The Italian raised her arms in triumph when she finally won a game after 37 minutes, and the crowd chanted "Sara! Sara!" in the hope of seeing a real contest, but Williams was having none of it.
A backhand return winner earned Williams her fifth break of the match, and she capped a superb performance in just 46 minutes with another totally dominant service game.