Mansell, who tested an LMP1 Ginetta-Zytek late last season alongside father Nigel, will partner Modena regular Antonio Garcia as the team makes the move from GT1 to GT2 with its new Ferrari 430.
It will mark a move away from single-seaters for the 24-year-old after spending the past two years in the Formula Atlantic championship, with his father also lending his experience to the programme.
"I think Leo is a natural for sportscar racing, he really took to the cars we tested last year," the 1992 F1 champion said of his sons deal. "The whole package has come together with the team, the Ferrari, Michelin etc, and we couldn't ask for a better team-mate. It will be a very exciting season, it will be my first visit to Le Mans and I am looking forward to it!"
Team boss Graham Schultz was quick to welcome Mansell into the team and said he was confident that his new driver line-up would be a strong pairing during the 2009 season.
"We are pleased to have Leo joining Team Modena," he said. "We are looking forward to a long relationship with Leo, and his partnership with Antonio Garcia should be a very strong one – Antonio has been a key part of Team Modena's international race success.
"Our link with Nigel is exciting, he will bring his huge experience of motorsport to bear on our programme and help us move to a new level."