Zouma spent last season on loan at Stoke City and will again spend the campaign away from Stamford Bridge after signing with the Toffees.
The defender's arrival continues a busy summer for Everton who have already signed Richarlison, Lucas Digne, Yerry Mina, Andre Gomes, Bernardo and Joao Virginia in the summer transfer window.
Zouma will wear the No. 5 shirt during his loan spell at Goodison Park, per the Everton website.
Everton managed Marco Silva has said the deal does not include an option to sign the defender permanently, per Phil Kirkbride at the Liverpool Echo:
The Frenchman moved to Chelsea in 2014 from French side Saint-Etienne. He was widely regarded as one of the most promising young defenders in Europe at the time.
However, his career at Chelsea was interrupted by a serious knee injury in 2016. He spent last season with Stoke where he was a regular for the Potters who ended the season by being relegated.
Before he moved to the Britannia Stadium he signed a new six-year deal with Chelsea which showed the club's faith in his ability.
New manager Maurizio Sarri has explained why he was keen to allow some of his players to leave this summer on loan, per Oliver Harbord at Football.London.
"Now I think the squad is too large, so I think some players have to go on loan," he said. "But I don't know who at the moment. I prefer to have 23-24 players, and three or four very young players. No more."
Chelsea have plenty of strength in defence with David Luiz, Gary Cahill, Andreas Christensen, Antonio Rudiger all ahead of Zouma in the pecking order.
The Blues will be hoping Zouma can see some regular game time at Everton this season in order to gain experience and continue his development.
Zouma will face competition for a place in the Toffees team. The club have invested heavily in signing Mina from Barcelona for £27.19 million, per BBC Sport.
The club also have Phil Jagielka, Michael Keane and Mason Holgate in the squad meaning Zouma will need to impress to force his way into Silva's starting XI.