Madigan was involved in the entire 2015 Six Nations, making substitute appearances in all five Tests. Ireland retained their title from the previous year, their 13th triumph in the competition. This was the first time that Ireland had retained their title outright since 1949, having shared the 1983 championship with France after winning in 1982. He celebrated his 26th birthday on the 21st of March, the same day Ireland were crowned northern hemisphere champions.