The 35-year-old will run a show race ahead of the French Grand Prix on June 27.
He will also test drive the car on June 29, exactly seven months after the crash in Bahrain.
"I am so happy to be able to drive an F1 car again.
Driving a title-winning Mercedes will be a unique experience, ”says Grosjean.
It was during Bahrain's GP 2020 that the Frenchman's car split in two and started burning.
Grosjean suffered burns to his hands in connection with the accident.
He chose to end his F1 career after the crash.
"I look forward to seeing him in France and welcoming him to the team," said Lewis Hamilton.
After the crash, Mercedes' stable manager, Toto Wolff, promised that Grosjean would be allowed to drive for Mercedes after the accident.
"We did not want the accident to be his last moment in an F1 car," says Toto Wolff.
During his F1 career, Romain Grosjean started 179 F1 races and ended up on the podium ten times.
ARCHIVE: Here the F1 driver cheats death - see the dramatic pictures (November 29)
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Formula 1 driver Romain Grosjean escapes from the burning car.
Photo: Viaplay