In 1619 Roth published a third part, under the title ‘De Processu Martyriali,’ and the entire work remains as an impeachment of English ecclesiastical policy in Ireland under Elizabeth and James I. An answer was published in 1624 by Thomas (afterwards Sir Thomas) Ryves [q. v.] This was the period of Roth's greatest literary activity.
Roth was appointed bishop of Ossory by Pope Paul IV in September or October 1618. The consistorial act describes him as ‘a priest of Ossory, forty-five years old, master in theology, protonotary apostolic, vicar-general of Armagh, in which post he has conducted himself well for several years, and worthy of promotion to the episcopate’ (Hibernia Dominicana, p. 869; Brady). He doubtless virtually ruled the diocese of Ossory for some years previously, as well as acting as deputy of Peter Lombard, the primate of Ireland, who never visited his see of Armagh. On 4 Sept. 1624 commendatory letters, signed by Roth as vice-primate, were sent from Ireland to all whom they might concern in favour of the Irish College at Paris, and of the Capuchin order (Spicilegium Ossoriense, i. 133–6). In a letter to Peter Lombard, dated 17 Sept. 1625 (ib. p. 137), he says that all in Ireland lived in dread of the plague, and that ‘few or no catholics die among so many that are on every side carried to their graves.’ The puritans, however, gave out that the plague was a judgment for the non-execution of laws against recusants.
In February 1629–30 Roth was one of seven Irish bishops who petitioned the Roman court for an increase of the hierarchy in England (ib. p. 164). Roth was no longer vice-primate, but he was senior bishop of Ireland, and was allowed a kind of leadership (ib. pp. 190–1). On 15 Nov. 1634 the bishop of Ferns wrote that Roth, though somewhat infirm, acted as a sentinel, keeping bishops, priests, and friars in order. ‘Some censure him as being over zealous, but in truth we stand in need of such a monitor in these regions of license and liberty’ (ib. p. 199). In May 1635 Roth was allowed to appoint Dr. Edmund O'Dwyer, afterwards bishop of Limerick, to represent his diocese at Rome (ib. p. 200). In July 1641 he felt the weight of years, and asked for a coadjutor (ib. p. 211); but he found time to attend to the diocese of Ferns, then vacant by the death of his friend and relative, Dr. Roche. Between September 1637 and 1639 Roth had been seeking to make peace in the diocese of Killaloe, where the clergy were on bad terms with their bishop. ‘Knowing,’ he wrote, ‘that the jars and strifes of my countrymen among themselves have from ancient times, at home and abroad, everywhere and always injured the whole nation, I have, during some thirty years' wrestlings in this arena, notoriously made it my chief work to make an end of useless altercations’ (ib. p. 235).
Until 1641 Roth lived quietly at Kilkenny. The Irish rebellion broke out on 23 Oct. of that year; the protestant clergy were expelled, and Roth took possession of the deanery, which he retained till just before his death. In 1642 the portreeve of Irishtown was sworn to him according to ancient custom. Kilkenny became the capital of the confederate catholics, and Roth was one of the bishops who signed the decrees of the great ecclesiastical congregation held there in May 1642 (ib. i. 262, in Latin; Confederation and War, ii. 34, in English). In June he signed a letter calling upon Clanricarde to make common cause with his coreligionists (Confederation and War, vol. i. p. li). In July he was one of those who petitioned the king, through Ormonde, for an audience, and begged him to construe their acts as those of loyal men against ‘the puritan party in England, who seek in all things to limit you, our king, and govern us, your people’ (ib. ii. 48). When the confederates formed their general assembly, Roth sat as a peer; but his age prevented him from being one of the supreme council, which was elected in October, and which directed everything until Rinuccini came. According to John Lynch [q. v.], he was the person chiefly instrumental in giving form and order to the confederacy (Graves and Prim, p. 295). After the cessation of arms with Ormonde in 1643, there was a meeting of bishops at Waterford for the purpose of announcing their full adhesion to the decrees of the council of Trent. Roth did not attend, but in January 1643–4 he signed the act of adhesion for himself and for the clergy of his diocese (Spicilegium Ossoriense, ii. 17). In this year Roth presented a silver-gilt monstrance, which still exists, to his cathedral of St. Canice ({sc|Graves}} and Prim, p. 40), and also erected a handsome tomb for himself in the lady-chapel, with an inscription recording that he had restored the church to its proper use and whipped heresy out of it. The reference to heresy was chiselled out by Bishop John Parry (d. 1677) [q. v.], but the rest of the memorial remains (ib. p. 293).
The nuncio Rinuccini reached Kilkenny on 12 Nov. 1645, and was met by the aged Roth at the door of St. Canice's. ‘He offered me the aspersorium and incense,’ says Rinuccini, ‘and, conducting me to the high
