He was an Irishman who had itinerated in America for two years under Francis Asbury. He was interviewed by John Wesley in England in September 1784. Wesley described him in a letter as 'an active, zealous man'. He was appointed as the first WM misionary to Newfoundland in 1785, following earlier initiatives by Laurence Coughlan, John Stretton and others. Newfoundland was still 'truly missionary ground', without roads, bridges or vehicles, with few horses, its children 'without education, the people without religious instruction, and the land without Bibles'. From his base on Conception Bay, McGeary travelled a circuit of 50 or 60 miles on foot. The church at Carbonear was built in his time, but controversy surrounded his efforts, and relationships between him and lay workers were poor.
In February 1787 John Wesley wrote to the Mission Superintendent William Black in Nova Scotia to say that McGeary was 'utterly discouraged' through 'want of the conveniences, yea necessaries of life'. In March 1788 he wrote again, asking Black to do what he could to keep the 'brethren in peace with each other'. In a direct reference to McGeary he commented: 'There is much good in him ... he is naturally of a bold, forward temper; but I hope his zeal is now according to knowledge.' McGeary married without obtaining the consent of his bride's father and withdrew from Newfoundland in 1788. But in 1791 Black found that McGeary had returned to Conception Bay the previous year. Black's visit led to improvements, with the organization strengthened, property questions resolved and some conversions taking place. However, by the following year, McGeary had again lost heart and returned to England. He was appointed to an English circuit in 1793, but withdrew the following year, providing 'a final proof of his unstable character'.