Beresford is the second surviving son of George de La Poer Beresford, 1st Marquess of Waterford, and his wife Elizabeth, only daughter of Henry Monck and maternal granddaughter of Henry Bentinck, 1st Duke of Portland. He attends Eton College and Christ Church, Oxford, where he graduates with a Bachelor of Arts in 1793 and a Master of Arts three years later.
Beresford is ordained a priest in 1797 and begins his ecclesiastical career with incumbencies at Clonegal and Newtownlennan. In 1799 he becomes Dean of Clogher and is raised to the episcopate as Bishop of Cork and Ross in 1805. He is translated becoming Bishop of Raphoe two years later and is appointed 90th Bishop of Clogher in 1819. He is again translated to become Archbishop of Dublin the following year and is sworn of the Privy Council of Ireland. In 1822, he goes on to be the 106th Archbishop of Armagh and therefore also Primate of All Ireland. He becomes Prelate of the Order of St. Patrick and Lord Almoner of Ireland. Having been vice-chancellor from 1829, he is appointed the 15th Chancellor of the University of Dublin in 1851, a post he holds until his death in 1862.
Beresford employs Lewis Nockalls Cottingham, one of the most skilled architects at that time, to restore St. Patrick’s Cathedral, Armagh. Cottingham removes the old stunted spire and shores up the belfry stages while he rebuilds the piers and arches under it. The arcade walls which had fallen away as much as 21 inches from the perpendicular on the south side and 7 inches on the north side, are straightened by means of heated irons, and the clerestory windows which had long been concealed, are opened out and filled with tracery.
Beresford dies on July 18, 1862 at Woburn, Bedfordshire, England, the home of his niece, in the parish of Donaghadee and is buried in the cathedral. There is a memorial to him in the south aisle at St. Patrick’s Cathedral, Armagh.