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.”
Johnson’s trial, to be held at Bradford Crown Court, is expected to last two weeks.