The 28-year-old footballer's contract was terminated hours after he was dropped for Saturday's Premier League match against Manchester United.
He will stand trial on Friday on two further counts of sexual activity with a child, which he denies.
Sportswear firm Adidas has cancelled its contract with the midfielder.
After Johnson's arrest in March 2015, the club suspended him, but then lifted the ban following talks with his representatives and the Professional Footballers' Association.
In his last appearance for the Black Cats, England international Johnson - who played while on bail - scored in a 2-2 draw against Liverpool at Anfield.
Johnson, who was born in Sunderland, began his career at Middlesbrough before moving to Manchester City and then to Sunderland for £10m in 2012.
When asked about the winger's future at a news conference earlier on Thursday, Sunderland manager Sam Allardyce said: "He'll not be available for this weekend. We will see how it goes after that."
The trial of Johnson, who has won 12 England caps, will take place at Bradford Crown Court and is expected to last two weeks.
Adam Johnson has been sacked by Sunderland after pleading guilty to one count of sexual activity with a child and one charge of grooming.