he was drafted onto the Ballygunner senior team. On 11 October 2009, he was just 18-years-old when he lined out in his first senior final. Lismore were the opponents, however, the game ended in a 4–12 to 2–18 draw. The replay a week later saw Mahony claim his first winners' medal following a 1–17 to 0–19 victory. On 29 November 2009, he lined out at right wing-back when Ballygunner suffered a 2–11 to 0–09 defeat by Newtownshandrum in the Munster final. Mahony lined out in his second final on 24 October 2010, with Ballygunner hoping to retain the title for the first time in 12 years. He scored a point from right wing-back but ended on the losing side following a 3–13 to 1–11 defeat by De La Salle. Ballygunner qualified for a third successive final on 16 October 2011, with Mahony once again lining out at right wing-back. He collected a second winners' medal following the 1–19 to 0–06 defeat of Tallow. Four final appearances in succession proved beyond Ballygunner, however, the club reached a fourth final in five seasons on 13 October 2013. Mahony was deployed at midfield but ended on the losing side for the second time in his career following a 3–16 to 3–13 defeat by first-time champions Passage. Mahony was back at right wing-back when he made his fifth final appearance on 5 October 2014. Ballygunner defeated Mount Sion by 2–16 to 0–09, with Mahony collecting a third championship winners' medal. On 18 October 2015, Mahony won a fourth Waterford Senior Championship medal following a 0–16 to 0–12 defeat of Tallow in the final. He later lined out in a second Munster final on 19 November 2015, however, he ended the game on the losing side following a 2–18 to 2–11 defeat by Na Piarsaigh. On 23 October 2016, Mahony lined out in a fourth successive final and made his seventh final appearance overall. He collected a fifth winners' medal from centre-back at the end of the game after the 4–20 to 1–12 defeat of Passage. On 22 October 2017, Mahony won a sixth Waterford Senior Championship medal when Ballygunner defeated De La Salle by 2–18 to 0–16 in the final. On 19 November 2017, he lined out in a third Munster final, however, in spite of being one of the stand-out defenders he ended on the losing side once again following a 3–15 to