Manby, Peter (d. 1697), dean of Derry, controversialist, and convert to Roman catholicism, was the son of Lieutenant-Colonel Manby. A scholar of TCD, he graduated BA in 1660 and on 23 November the same year was appointed to a minor canonry of St Patrick's cathedral, Dublin, from which he resigned in 1661. He was prebendary of Lisclery, Co. Cork (1663–5), rector of Ardnegihy and vicar of Cannaway, Cork (1663–6). Having graduated MA, he was appointed chancellor of St Patrick's cathedral on 9 April 1666 and personal chaplain to Michael Boyle (qv), archbishop of Dublin. It was during Boyle's triennial visitation in 1670 that Manby was collated canon of Kildare and on 21 December 1672 he was installed as dean of Derry.
Manby's first publication, A letter to a nonconformist minister, was printed in London in 1677, and in 1682 his Ash Wednesday sermon, concerning abstinence during Lent, preached at St Patrick's that year, was published in Dublin. His conversion to Roman catholicism in 1686 was attributed by his critics to his failure to obtain the bishopric of Derry. On 21 July 1686 James II (qv) indicated his approval by granting him a dispensation under the great seal of England to retain the deanery of Derry. Another of Manby's publications, Of confession to a lawful priest: wherein is treated of the last judgment, was printed in London in 1686, but it was the publication in 1687 of The considerations which obliged Peter Manby, dean of Derry, to embrace the catholique religion for which he became known. This apologia precipitated a controversy with William King (qv), chancellor of St Patrick's and later archbishop of Dublin. King published a reply to Manby's ‘considerations’ and the dean responded with another publication, A reformed catechism in two dialogues, concerning the English reformation . . . published for the information of the people, printed in London and Dublin in 1687. King countered with A vindication of the answer to the considerations, and Dr William Clagett added his Several captious queries concerning the English reformation, first proposed by Dean Manby . . . briefly and fully answered (London, 1688). James II again showed his support for Manby by making him an alderman of Derry in 1688. Following James's defeat at the Boyne in 1690 Manby retired to France and then to London, where he died in 1697, attended by Dr Cornelius Nary (qv).
Manby had at least one brother, Robert, whom he influenced to join the catholic church. The Derry cathedral register recorded the baptism of Peter's two nephews, John and Peter, on 9 May 1674 and 11 January 1677 respectively; they both went on to become Jesuits. A Peter Manby, apparently born in Leinster in 1681 and educated at Coimbra, published Remarks on Dr Lloyd's translation of the Montpelier catechism (Dublin, 1724), a critique of the catechism's erroneous contents attributed to Jansenius and Quesnel.