He was chosen to fill the post of Chancellor of England under Simon de Montfort, at whose death, however, he was deprived of the office. It was some years after this that he became Bishop of Hereford, and was consecrated at Canterbury, September 8th, 1275. No Welsh bishop attended the consecration. After he became a bishop he still wore his hair-shirt and showed ever intense devotion in his celebration of divine service. He was remarkable in the steadfastness and ability he displayed in maintaining the rights of the see. Gilbert de Clare, Earl of Gloucester, claiming a certain "chace" near Malvern Forest, whence came the Bishop’s supply of game, found a relentless opponent in Bishop Cantilupe. The Bishop was prepared with the customary "pugil" or champion (who received 6s. 8d. per annum), though his services were not required. The Earl was excommunicated, and appealing to the law in a trial Bishop Cantilupe eloquently maintained his right to capture "buck, doe, fawn, wild cat, hare, and all birds pertaining thereto," and as a result of the verdict being in his favour, caused a long trench to be dug on the crest of the Malvern Hills as a boundary line, which is still traceable. Llewellyn, King of Wales, was made to restore three manors of which he had obtained unlawful possession; and Lord Clifford, for cattle-lifting and maltreating the Bishop’s tenants, was compelled to walk barefoot to the high altar in the cathedral, while the Bishop personally chastised him with a rod. Many cases did he fight out successfully, but his greatest struggle was on a question of testamentary jurisdiction with Peckham, Archbishop of Canterbury, by whom he was ultimately excommunicated and obliged to leave the country, attended by Swinfield, his faithful chaplain. He obtained a decree in his favour from Pope Martin IV., but died on the homeward journey on August 25th, 1282. He was buried in the church of St. Severus, near Florence; but his bones having been divided from the flesh by boiling, were later carried to England and solemnly placed in the Lady Chapel of the cathedral. It is said that the Earl of Gloucester, with whom Bishop Cantilupe had had the dispute about the chace, attended the ceremony, and that blood began to flow from the bones when he approached the casket containing them; upon which the Earl immediately restored the property he had taken unjustly from the church. Forty years later Bishop Cantilupe was canonised. It is said, amongst other evidences of his saintliness, that he never allowed his sister to kiss him. Three hundred sick people are said to have been cured at the place of his interment, and so many candles were presented by the crowds of visitors that Luke de Bray, the treasurer of the cathedral, had a dispute with the prebendaries as to the value of the wax, two-thirds being finally assigned to the treasurer and one-third to the prebendaries.