At the beginning of the 2017–18 season, his final year in the academy, O'Donnell joined Buccaneers who had recently been promoted to Division 1A of the All-Ireland League. O'Donnell played with the Pirates when available, but also missed league matches to play with the Connacht Eagles. In January 2018, he made his return to the senior Connacht team when he featured from the bench against Munster in the Pro14. In March 2018, it was announced that O'Donnell had signed a senior contract with Connacht for the following season.