Beresford was returned for county Londonderry, as soon as he came of age, by his brother the 2nd Marquess of Waterford, who had represented it in the last ten years of the Irish parliament. As a member of the Beresford squad, he was an indifferent supporter of Addington’s administration, voting against it on Pitt’s defence motion, 25 Apr. 1804, and subsequently rallying to Pitt’s second ministry.
Beresford voted against the repeal of the Additional Force Act by the Grenville ministry, 30 Apr. 1806, the only Member of his connexion to attend, but subsequently abstained; ministers were keen not to alienate his family and came to terms with his brother, which secured his support and theirs for him.
In March 1811 he was given first refusal of the constableship of Dublin Castle, but he did not wish to vacate his seat for it.
