On 8 July 1715 he was appointed to the position of Archbishop of Armagh. Hugh MacMahon was the first of three Clogher bishops who were, in succession, appointed to the See of Armagh.
Hugh MacMahon was appointed Archbishop of Armagh on July 8, 1715, and this position was later held by three other Clogher bishops who took turns occupying the See of Armagh.