The 36-year-old had been a free agent since leaving Inter Milan at the end of June and began training with Bologna at their Casteldebole base while Raffaele Palladino assessed his fitness.
Darmian was brought in after Emil Holm suffered a serious hamstring injury while playing for Sweden. The Bologna defender underwent surgery and is expected to be sidelined for four to six months, leaving the club looking for additional defensive cover.
Darmian had initially been given several training sessions to prove he was ready to return to competitive football after spending the opening months of the season without a club.
That assessment has now been completed, with Bologna deciding to proceed with the move.
The agreement will run until the end of the current season, with an option allowing the club to extend Darmian’s contract through June 2028.
Darmian also featured in a behind-closed-doors friendly against Ascoli during his period with the squad. The game provided another opportunity for the coaching staff to assess his physical condition before the final decision was made.
Bologna had identified the Italian as their preferred option to strengthen the defence after Holm’s injury, although Elseid Hysaj had also remained under consideration as another available free agent.
Darmian brings extensive experience from a career that has included spells with Milan, Palermo, Torino, Manchester United, Parma and Inter. He spent the previous four seasons with Inter and made more than 200 appearances for the club across all competitions.
His versatility was another factor in Bologna’s decision. Darmian can operate on either side of the defence and has also played as part of a back three, giving Palladino another experienced option as he works with the squad.
Bologna’s initial agreement was subject to Darmian passing the club’s physical assessment. After his training period produced positive results, the club moved ahead with the signing.
The move gives Darmian a return to Serie A and Bologna a short-term solution for a position weakened by Holm’s lengthy absence. The option for another season also gives the club the opportunity to retain him beyond June if the arrangement proves successful.