Rybakina, the world No.4, hit 10 aces and saved 11 of the 13 break points she faced to win their semi-final at the clay-court tournament in two hours, 49 minutes.
It's Rybakina fourth win in six meetings with Swiatek. The Pole was bidding to become the first three-time champion in Stuttgart since Maria Sharapova from 2012-14.
Rybakina will play Marta Kostyuk in Sunday's final after the 27th-ranked Ukrainian defeated Wimbledon champion Marketa Vondrousova 7-6 (7-2, 6-2 in the other semi-final.
It will be Rybakina's fifth final of the season. She won titles in Adelaide and Abu Dhabi.
Swiatek was under constant pressure on serve from Rybakina. She faced 20 break points and lost four of them. Seven double faults and 42 unforced errors didn't help.
"Since we played with Iga many times, more or less I try to predict where she's going to (serve), and (I'm) really happy with the return and overall with the game," Rybakina said.
Kostyuk has surprised herself with her run to the final, including three consecutive wins over top-10 players Zheng Qinwen, Coco Gauff and Vondrousova. Kostyuk saved match points against Zheng and Gauff.
"I came here on Saturday and I practiced four days before my first match, and really I was playing worse and worse with every day," Kostyuk said. "I was like, 'OK, time to play some matches because I don't want to practice anymore.'"
Kostyuk will appear in her third final. She won her maiden title in Austin last year, and was runner-up in San Diego last month.
She and Rybakina are 1-1 in career matchups.
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