The 25-year-old was happy to leave the Turin giants and Thomas Tuchel offered him a route out of Serie A during a frantic end to a record-breaking summer transfer window at Stamford Bridge.
Having already spent a club and British record during a single window, the Boehly-Clearlake Capital partnership continued to back Tuchel deep into the final hours of the window. A loan move has been rushed through and the club have an option to buy next year for £26m.
Zakaria only joined Juve in January after running down in his contract with Borussia Monchengladbach, making 15 appearances for the Italian giants.
The Swiss international emerged as a late target after Chelsea were blocked in their attempts to sign Ajax midfielder Edson Alvarez. A £40m offer was rejected, while PSV Eindhoven also snubbed the Blues after they made an approach for Ibrahim Sangare.
Tuchel is currently without N’Golo Kante and Ruben Loftus-Cheek in central areas, while Mateo Kovacic is not fully fit.
It was a busy day for the midfield department in south west London, with Billy Gilmour joining Brighton on a permanent transfer.