The creative midfielder was picked up for circa €5-6m and signed a contract to June 2025.
However, he will immediately be sent out on loan to fellow Serie A side Sampdoria in order to gain experience.
Ihattaren turned 19 in February and has 74 appearances in the PSV shirt already, with 10 goals.
Hellas Verona had also been interested in taking him on loan, but Sampdoria got the deal done for a one-season dry loan.
Born and raised in the Netherlands with joint Moroccan citizenship, Ihattaren has Dutch caps at various youth levels and is now on the outskirts of the senior squad too.
— JuventusFC (@juventusfc) August 31, 2021