The winger was suspended by the club following his arrest earlier this month on suspicion of sexual activity with an under-aged girl.
Johnson’s bail was this week extended until April 23, prompting Sunderland to review the suspension, and he will now be allowed to train pending the outcome of the police investigation.
A statement read: “The club has discussed the current position in detail with both the Professional Footballers’ Association and Adam???s representatives.
“In line with those discussions we recognise that the player is entitled to re-commence his duties with the club while the legal process continues. He will therefore return to training.
“The club???s own investigation cannot continue until the conclusion of the legal process. Sunderland AFC will make no further comment on the matter due to the ongoing police investigation.”