— JuventusFC (@juventusfc) September 22, 2020
Morata, 27, returns for a second spell with Juve after previously wearing the black and white from 2014 until 2016.
Atletico will receive a €10m loan fee from Juventus, who can buy Morata for €45m at the end of the season.
Alternatively, Juventus can loan Morata for a second year for another €10m loan fee.
They would again have the option to buy the Spaniard at the end of the 2021-22 season for €35m.
It ends Andrea Pirlo’s hunt for a new striker, which saw many big names linked with the Serie A champions.
Morata returns to Turin after two seasons at Atletico Madrid, who he joined from Chelsea in 2018.
His exit will pave the way for Luis Suarez to join Atletico from Barcelona after the two clubs agreed terms on Tuesday night.