Pollock, John (d. 1825), attorney and clerk of the crown for Leinster, was the third son of John Pollock (1718?–85), a linen merchant of Newry, Co. Down, and his wife Elizabeth, daughter of Robert Carlile of Newry. John Pollock the elder, who had six other sons and four daughters, established a bleaching green at a place north of Newry which he called Bessbrook after his wife. His father, Robert (d. 1741 or 1742), purchased Ballyedmond, near Newry (1732), and had another son, James, father of Joseph Pollock (qv) the barrister. Of the upbringing of John Pollock the younger nothing has been ascertained. Admitted as an attorney (1775), he soon had a flourishing practice at the law courts in Dublin; he had an address in Mary St. (c.1777), in Anne St. (until 1784), in Jervis St. (until 1801) and then at 11 Mountjoy Sq. (until 1817). He became a Freemason, a member of the Orange (no. 257) lodge, which met in Belfast (October 1783). From the mid 1780s he held lucrative official positions, one of them solicitor to the Linen Board (1785–94). He owed his wealth and influence to his being adviser and friend to Arthur Hill (qv), who succeeded in 1793 as marquis of Downshire.
An acquaintance of William Drennan (qv), whose democratic politics he did not share, Pollock twice attempted without success to persuade Drennan to keep him informed about the activities of the United Irishmen (November 1792). At the same time he was, Drennan believed, behind attempts to entrap Archibald Hamilton Rowan (qv) by directing agents provocateurs. From 13 March 1794, Pollock was clerk of the crown and peace for Leinster at £500 p.a. in addition, so Drennan believed, to ‘£2,000 a year under government for his espionage’ (Drennan–McTier letters, ii, 49). In April 1796 he inherited an estate at Mountainstown, Co. Meath (said by Drennan to be worth £1,000 p.a.), from Samuel Gibbons (1728–96), who died heavily in debt. This he did having gathered, by investing some of Downshire's money, almost all of the encumbrances. A few months later he and the marquis of Downshire took part in the arrests in Belfast of Samuel Neilson (qv), Thomas Russell (qv) and other United Irishmen (16 September 1796). By the end of 1796, when rebellion and French invasion threatened, he was regularly directing and paying informers such as Leonard MacNally (qv). In the aftermath of the rebellion of 1798 he had an important role in deciding the fate of state prisoners.
In 1809 he advised the chief secretary, Arthur Wellesley (qv), later created duke of Wellington, that ‘catholic emancipation is wholly, with the great body of the catholics, a cloak to cover their real object’, which he believed to be ‘the political power, the church estates and the protestant property in Ireland’ (Civil corr., 535). In 1800, Pollock was appointed deputy clerk of the pleas of the exchequer, a sinecure worth about £5,500, double by 1816, when it was stated in parliament (29 April) that he had misappropriated £10,000 from the office. In consequence he was deprived. His name no longer appeared in Wilson's Dublin Directory after 1817. According to the historian of the Pollock family, John Pollock died 18 December 1825 at Mountainstown. He left, by his wife Hannah Maria (d. 1826), eldest daughter of George Clarke, a London banker, an only son, Arthur Cornwallis (1785–1846), who as a young man travelled in Russia before settling for the life of a country gentleman in Co. Meath.