Johnston, John (1786–1862), presbyterian minister, was born at Aughendrummond, Clogher, Co. Tyrone, seventh son of William Johnston, farmer and merchant; his mother may have been his father's second wife, Margaret (née Armstrong?). He was educated at Mr Millar's school at Clogher and at Glasgow University. One of his fellow students there was Dr Henry Cooke (qv), who in his memoirs recorded how Johnston always fell on his knees to thank God after they had made the then perilous crossing from Donaghadee to Portpatrick. He was licenced to preach by the Clogher presbytery in 1806 and ordained in Cootehill in 1808. After just three years he was installed in Tullylish, Co. Down, where he ministered for over fifty years. He was moderator of the general assembly in 1858, in which year he also received an honorary doctorate in divinity from Princeton, New Jersey, USA. His moderatorial year was marked by sectarian riots in Belfast, and on one occasion he adjourned the assembly for a full afternoon so that prayers might be offered for peace and renewal. The next year saw the great revival of 1859.
Johnston's name was best known for his outreach work in organising open-air preaching. He was the assembly's convenor in this aspect of evangelism from 1844 to 1855. He figured prominently in the dispute over the legality of presbyterian marriages following the test case of Regina v. Millis in 1836. The marriage in question, performed by him in Tullylish, led to a trial at the queen's bench in 1842 and then at the house of lords. It resulted in the passing of a bill in 1844 which removed the grievance in presbyterian eyes.
He married first (1817) Frances (d. 1838), daughter of John Jackson of Creive House, Ballybay; they had a daughter and four sons. He married secondly (1849) Grace, daughter of Francis Lascelles of Newry. Two of his sons were well known philanthropists: the Rev. Dr William Johnston (qv) of Townsend St., Belfast, founder of the Presbyterian Orphan Society, and Dr Henry Martyn Johnston, physician, who set up the Belfast sick-poor fund. John Johnston died on 16 October 1862 after returning from London, where he had visited his daughter and son-in-law, Dr Francis Graydon Johnston, who was his medical adviser. He was buried beside his church at Tullylish. There is a pencil sketch of him in McComb's Presbyterian Almanac (1859) and a portrait in Presbyterian Church House, Belfast.