The Nigeria international was earlier pictured undergoing a medical at the club's home base, and has now confirmed his departure from the London club.
In a statement published on his official Twitter page, the midfielder wrote: "As you will know, I haven't featured as much this season as I would have liked, and at 29 I still have many years in the game ahead of me.
"With this in mind, I feel now is the time to seek a new challenge.
"I'm delighted to be joining Tianjin TEDA FC in China, at a time that the Chinese Super League is really taking off, and I look forward to helping Tianjin TEDA FC continue to grow both on and off the pitch in the next few years.
"To everyone at Chelsea goodbye, and thank you. You will always be part of who I am, and I wish you the best of luck.
"I could not be happier saying goodbye with the club back where it belongs - top of the league.
"Keep The Blue Flag Flying High!"
The midfielder becomes the latest big name player to join the Chinese Super League gold rush after failing to force his way into Antonio Conte’s Chelsea side.
Mikel had a medical in the port city of Teda some 130 kilometres from Beijing on Thursday and the Asian Football Confederation confirmed the deal on Friday.
The 29-year-old Mikel, who spent more than a decade at Stamford Bridge, was given a free transfer by the London club and will earn £140,000 a week in China, according to local media reports.
Mikel previously played for Norwegian club, Lyn Oslo before his move to Chelsea in 2006.
A letter to my Chelsea family. ???? pic.twitter.com/FhcUyq3iaV— Mikel John Obi (@mikel_john_obi) January 6, 2017