In 1620 after a period as Vicar General Arthur was appointed bishop and he received consecration in 1623 where the principle consecrator was bishop Rothe of Ossory. Arthur was already 63 when consecrated and was never in great health. After being bishop for seven years he asked Rome for a coadjutor. An assistant was not forthcoming though so he had to labour on in difficult circumstances. In the final years of his life Limerick was besieged twice during the Confederate period. Despite the difficulties the Confederate period was one when Catholics could function open and freely so Arthur was able to welcome Capuchins and Jesuits to Limerick. During this period the Papal Legate Archbishop Rinuccini was able to visit Limerick and assess the situation. Rinuccini was in Limerick in 1646 when Arthur died and he describes his death in his memoirs, the Commentarius Rimiccinianus.