He made a move to Asia in January 2017 after spending over 10 seasons at Stamford Bridge.
During his time in west London he made 374 appearances and collected numerous major honours.
That considerable experience is now about to be added to the fold at the Riverside Stadium as he seeks to help Boro secure a return to the top tier in England.
Tony Pulis told the club’s official website after completing a prized capture: "I'm pleased to get him in. He is a man with a lot of experience and quality.
"He has a winning mentality and he wants to be here and a part of what we are looking to achieve."
Mikel has linked up with Middlesbrough as a free agent.
He has been without a club since the end of the Chinese Super League season in November, with the decision taken to sever ties with Tianjin TEDA.
The 31-year-old now has a new challenge and a fresh start on his hands.
A number of clubs from across Europe had been credited with holding an interest in putting terms to a seasoned performer.
He has been handed the No. 2 shirt and becomes Boro’s second signing of the winter transfer window following the arrival of Rajiv van La Parra on loan from Huddersfield.
Mikel has made his way to Teesside with Pulis’ team sat fifth in the Championship table, six points adrift of the automatic promotion places.