John McGregor, born in Scotland, was a soldier in the 42nd Highlanders. He fought in the Battle of Fontenoy (1745) and in the Siege of Bergen op Zoom (1747). Some years later he was drafted with a detachment of his regiment to the garrison at Limerick, and c. 1760 joined the Methodist society there. He resigned from the army, married and settled in Limerick, where he was for many years a class leader.
In 1790 it was reported that he was a member of the select band. He continued to meet his class in his room, and often conducted the meetings from his bed. His leadership was so highly valued that the members would not let him give up, as he said, 'until I am removed to my heavenly Father, which I expect will not be long.'Waterford Herald, a paper which first appeared three years earlier and has been described as 'a short-lived newspaper of no recognisable politics or polemics'. It was published three times a week at a price of 2½ pence. The last known issue was that of 10 March 1796. He edited the Munster Telegraph for a short period around 1794, but no records of this paper have been traced.
Always an ardent Methodist, when the Irish Methodists divided in 1818 over the question of their relationship to the (Anglican) Church of Ireland, J. J. McGregor allied himself with Primitive Wesleyan Methodists who maintained their links with the Church, and in 1823 became the first Editor of the Primitive Wesleyan Methodist Magazine, a post he held until his death.
In 1821 he moved to Dublin, but his name does not appear in the Dublin Directories until 1834, when he is shown as living at 31, Mountpleasant Terrace in the Ranelagh area. A prolific writer, his publications include an 11-volume History of the French Revolution, a History of the County and City of Limerick, and True Stories from the History of Ireland. Remarkably, in the year in which he moved to Dublin he wrote The New Picture of Dublin: or Stranger's guide to the Irish metropolis: containing a description of every public and private building worthy of notice, and a correct account of the various commercial, benevolent and religious institutions. To which is added, a brief notice of the various pleasure tours round the metropolis.
He died on 24 August 1835, and was interred in the graveyard of St. Patrick's Cathedral. His son, also John James McGregor, was born in Waterford. He studied medicine at Edinburgh University, and gained the degree of MD in 1833. The title of his thesis was 'De Inflammattione'. He established a practice at Grafton Street, East in London.