The 27-year-old Spain international returns to Allianz Stadium, where he starred between 2014 and 2016 and scored 27 goals in 93 appearances, winning two Scudetto titles along the way.
Juventus were in need of a striker after terminating the contract of Gonzalo Higuain, who has since joined Inter Miami in the Major League Soccer.
Andrea Pirlo’s side opened their Serie A campaign without a recognised center forward, winning 3-0 against Sampdoria on Sunday.
The Old Lady had been linked with moves for AS Roma’s Edin Dzeko and Barcelona’s Luis Suarez but have instead settled on Morata.
Juventus have the option to make Morata’s move permanent at the end of the season for €45m or pay €10m to the extend the loan deal for another season before sealing a €35m move at the end of the 2021/2022 season.
Juventus' statement on their club website announcing the transfer said: "There’s nothing more exciting than a homecoming and the return of Alvaro Morata to Turin is a beautiful one at that!
"Alvaro Morata had only spent two years at Juventus, before Real Madrid recalled him to the Spanish capital. However, a lot can happen in two years and Alvaro certainly left an album of memories, filled with many spectacular moments: goals, celebrations, victories and trophies!
"Memory albums are there to be opened, to reminisce upon old moments, but also to add new ones and we can’t wait to create many more memories, together once more!"
Morata’s exit from Atletico Madrid has paved the way for Diego Simeone’s side to conclude a deal for Suarez.
