A statement from the club read:
"In light of Adam Johnson's guilty pleas, the club has today terminated his contract with immediate effect."
Earlier in the week, Adidas had also cancelled its contract with him over the Child Sex charges.
Johnson pleaded guilty to one count of sexual activity with a child and one count of grooming at Bradford Crown Court today.
The 28-year-old appeared in court on the first day of his trial into allegations of child sex charges relating to incidents between December 2014 and February last year.
England international Johnson denies two charges of sexual activity with a girl under the age of 16.