The 24-year-old’s contract with Paris St-Germain expired on 30 June, leaving him free to sign for rival clubs.
PSG coach Thomas Tuchel refused to pick Rabiot from December last year after it became clear he was not willing to extend his stay at the club.
In 2018, Rabiot refused to be named on France’s standby list for the World Cup after not being picked in the squad.
Rabiot will become Juventus’ second free transfer signing of the summer, following Wales midfielder Aaron Ramsey, who ended his 11-year at Arsenal to move to Turin.
Meanwhile, Lille have signed United States international winger Timothy Weah, 19, from PSG on a five-year contract.