Mikel, who arrived at the club around 11:15 am on Monday, was announced after a successful medical check-up.
Mikel is now Stoke City’s fourth signing of the summer.
Mikel, who won a host of domestic and European honors during a glittering 11-year stay at Chelsea, returns to English football after a spell in the Turkish Super Lig with Trabzonspor.
Manager Michael O’Neill said: “We’re delighted to bring John to the Club. His playing career speaks for itself and underlines his calibre as a player.
“I was really impressed with him when we met for the first time and he outlined what he wants from the next phase of his career.”
“We spent four hours talking and he made it clear he wants to get back into the Premier League and finish his career there and hopefully he can do that with Stoke City.”