Morbidelli joins from Yamaha as teammate to Spaniard Jorge Martin (25), who is second in the championship standings. He will replace the LCR Honda-bound Johann Zarco (33).
"It is an honour to have the opportunity to work with a champion like Franco," team manager Gino Borsoi said.
"I have great confidence in him and his talent. I am sure that he will fit in very well in our team and that together we will be able to achieve great results."
Morbidelli was championship runner-up to Spaniard Joan Mir (26) in 2020 when he won three grands prix but he has not won a race since then.
Yamaha last month announced he would be leaving the team, with Alex Rins (27) taking his place.