The Wearside club had initially left the winger out of their squad for this weekend's Premier League clash with Manchester United but it has since been confirmed that they have parted ways with the player.
Johnson, 28, recently pleaded guilty to one charge of sexual activity with a 15-year-old girl and one count of grooming. He denied two further charges of sexual activity with a minor.
The former Middlesbrough and Manchester City attacking midfielder appeared in Bradford court on Wednesday where he pleaded guilty, a call that could ultimately cost him his career, and see him end up in jail.
"The club will make no further comment."
The 12-time England international arrived at the Stadium of Light in 2012 and made a total of 141 appearances for the Black Cats, scoring 22 goals.