The 28-year-old had previously admitted to grooming a 15-year-old girl and one charge of sexual activity with her, relating to an incident when he kissed her in his Range Rover.
He was cleared of one more serious charge of sexual activity with a child regarding an oral sex act, but found guilty of a second charge of sexual touching by a majority verdict of 10-2.
The judge at Bradford Crown Court said a custodial sentence was "almost inevitable" and told Johnson he was likely to face a jail term of between four and 10 years.
The former Sunderland player was granted bail and will be sentenced in two to three weeks.
Johnson, who wore a black suit, white shirt and black tie, sat in the dock between two security guards and did not appear to react to the verdicts.
The charges related to an incident that occurred after he picked the girl up in County Durham, northeast England on January 30 last year.
The girl was a Sunderland fan who would wait for Johnson outside the club's stadium after home games and began exchanging messages with him after he accepted her Facebook friend request.
The trial heard that the pair exchanged 834 messages using the WhatsApp messaging service, during which she made it clear how old she was.
They subsequently met on two occasions, on January 17 and January 30, and it was on the second occasion that the sexual touching for which Johnson was convicted took place.
Johnson was sacked by Premier League employers Sunderland last month after pleading guilty to the count of grooming and the first count of sexual activity with a child on the first day of his trial.
He had been playing for Sunderland until the weekend before the trial began, having initially been suspended following his arrest.
In a statement released after the verdicts were announced, Sunderland "refuted in the strongest possible terms" the suggestion that they had known Johnson would change his initial not guilty plea to guilty at the last minute in order to play for the club for as long as possible.
"The club was NOT advised in advance that Mr Johnson would plead guilty to any offence," Sunderland said.
"Had the club known that Mr Johnson intended to plead guilty to any of these charges, then his employment would have been terminated immediately.
"Indeed, upon learning of the guilty plea on 11 February 2016, the club acted quickly and decisively in terminating Adam Johnson's contract without notice."
Johnson began his career with Middlesbrough and returned to his native northeast in 2012 when he joined Sunderland from Manchester City in a £10 million ($15.3 million, 13.7 million euros) transfer.
He has been capped 12 times by England, making his last international appearance in February 2012.
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