The Australian, who has competed in the America's Cup since 2000, was officially named as a new member of Luna Rossa overnight.
"With his huge sports and technical experience on high-performance sailing boats, Jimmy brings additional strength to team Luna Rossa," the team's official website said.
Spithill was at the helm of Luna Rossa's loss to Emirates Team New Zealand in the 2007 America's Cup, before he made the move to Oracle Team USA where he won the event in 2010 and 2013.
The 2013 victory was where he helped stage one of the biggest comebacks in sport, coming back from 8-1 down to defeat Team New Zealand.
With Oracle Team USA unlikely to be involved in the 2021 regatta, Spithill returns to his Italian team mates in a bid to stay in the game.
Italian publication Ventro e Vele reported that Spithill had recently been spotted in Cagliari, Sandinia where Challenger of Record Luna Rossa have set up base.
Luna Rossa, who have collaborated closely with Team New Zealand on the monohull class rule, pose as serious contenders in the 2021 regatta.
