The defender who left the club two seasons back for a world record transfer fee of £50 million to the French club is back to Stamford Bridge.
Both the clubs confirmed the news of their Twitter handles as well as on their official websites.
Chelsea FC's tweet read:
PSG's Tweet read:
PSG's official statement read: "Chelsea Football Club and Paris Saint-Germain have agreed terms for the transfer of David Luiz back to London."
Chelsea FC's official statement read: "David Luiz is a Chelsea player once more having completed a return to Stamford Bridge following two years at Paris Saint-Germain."
After re-joining the club, speaking to the club website, the 29-year-old Brazilian centre-back said: "I'm delighted to return to Chelsea.
"We had a fantastic story during my first time at the club and I want to help the team and Antonio Conte achieve a lot of success.
"I always had a wonderful relationship with the fans and I am looking forward to wearing the blue shirt at Stamford Bridge once again."
David Luiz was Chelsea's second signing on the deadline day. Earlier the Blues had signed defender Marcos Alonson from Fiorentina.