In 1824, Beresford was ordaineddeacon and in 1825 priest, and was quickly appointed Rector of Kildallon, County Cavan, a parish in his father's diocese of Kilmore. Three years later, he was preferred to the vicarages of Drung and Larah in the same diocese, benefices which he held until 1839 when he became archdeacon of Ardagh when Ardagh was united with Kilmore. His father was succeeded by Bishop Leslie, but on Leslie's death in 1854 Beresford followed in his father's footsteps as bishop of Kilmore and Ardagh and was consecrated in Armagh Cathedral on 24 September 1854.[1]
In the Church, Beresford gained the reputation of being a statesmanlike presence during the storms which were caused by William Ewart Gladstone's measures to bring about disestablishment of the Church of Ireland, playing a large part in the negotiations this called for, and then afterwards had the hard task of reconstituting the church.[1]
On 25 October 1824 Beresford married Mary, a daughter of Henry L'Estrange of Moystown and the widow of R. E. Digby of Geashill. They had two sons and three daughters: Charlotte Henrietta Beresford (died 1884), Mary Emily Beresford (died 1858), George De la Poer Beresford (1831–1906) and Major Henry Marcus Beresford (1835–1895).[1][2]
Beresford's first wife died in 1845, and on 6 June 1850 he married secondly Elizabeth, daughter of James Trail-Kennedy of Annadale, County Down and the widow of Robert George Bonford of Rahenstown, County Meath.[1][2]
There is a memorial to Elizabeth in the south aisle at St Patrick's Cathedral, Armagh.[5]
