Luiz won the Champions League, Europa League and FA Cup in his three years at Chelsea after joining from Benfica in 2011.
"It's fantastic to have this second opportunity to play for this club. I love this club, that's why I am here," Luiz told www.chelseafc.com.
"It will be an amazing opportunity to show the fans again how I love this club. I cannot wait to wear the shirt and play at Stamford Bridge again."
Luiz, who won two consecutive Ligue 1 crowns with PSG, said he wanted to fight for more trophies with Chelsea.
"Of course I want to win the Premier League and of course I want to win all the titles again," he added.
"I am here because I have ambition to play for a big club and when you play for a big club you need to think about winning every single match."
Luiz could feature in Chelsea's next game at Swansea City on Sept. 11.
(Reporting by Ian Rodricks in Bengaluru; Editing by Tony Jimenez)
