The 30-year-old arrived in Turin on Wednesday and began his medical, which was then completed on Thursday prior to him signing a three-year contract with the Italian champions.
The deal could rise to €30.5m if certain appearance-related bonuses are triggered during Matuidi's time with the club.
Juve have been active in the transfer window, with Matuidi's arrival adding to the likes of Federico Bernardeschi, Wojciech Szczesny, Mattia De Sciglio and Douglas Costa.
Matuidi spent six seasons at PSG and was a key performer throughout his spell, winning Ligue 1 four times among 16 domestic trophies.
His departure comes as PSG look to balance the books following their world-record €222m signing of Neymar from Barcelona.