The deal sees the Juventus holding midfielder join up on a loan spell.
There is a buy option clause inserted in the deal should Chelsea be satisfied with his performances this season.
Personal terms for the player has already been agreed.
Zakaria will seek to make an instant impression at Stamford Bridge haven seen his spell at Juventus turn out so-so.
The signing will be Chelsea’s second of the transfer deadline day, with Aubameyang crossing the line already from FC Barcelona.