In April 2015, he signed a one-year contract to play for Leinster. He made his return for Leinster against Edinburgh Rugby in the 2015-16 Pro 12 season kicking 9 points. The following week, he was the stand-in captain and he kicked 13 points to help Leinster beat Cardiff Blues. He played at fullback in both games. Nacewa extended his contract and was installed as the Leinster Captain for the 2015/16 season. Nacewa was named captain of the Pro 12 team of the season as he led Leinster to the top of Pro 12 table and the final at Murrayfield where they were defeated by Connacht Rugby 20-10.