He was born in Co. Galway on 3 June 1831, the son of a Methodist minister, William Guard (e.m. 1821; d. 1850). After nine years in Irish circuits he ministered in South Africa and America. His wife's health was a factor in these appointments. Letters from South Africa in 1869 and 1870 reveal that he was unsettled, but did not wish to return to Ireland or Britain. A request to the Missionary Committee to be allowed to lecture and preach in Australia was refused. A visit to America to raise money for a new church in Port Elizabeth led to periods of ministry in Baltimore from 1872, San Francisco from 1875, Oakland, Calif. from 1878 and Baltimore again from 1880. He died suddenly on 15 October 1882, when about to take up an appointment in Philadelphia.
A volume of Lectures and Addresses was compiled and published in 1885, containing fifteen lectures and addresses by Guard and a memorial sermon delivered two weeks after his death. Some of the lectures had already been published, including 'The Mental Activities of the Age and the Bible', delivered in Boston, 'The Sovereignty of Man', in San Francisco in 1879, and a 'Masonic Oration' in California in 1878. A few had first been given in South Africa, including the earliest for which a date is given, in Graham's Town in 1864.
His two brothers also entered the ministry: Edward (born at Letterkenny on 29 April 1833; e.m. 1856; died on 22 April 1884) and Wesley (born at Limavady, 1839; e.m. 1862; died on 10 February 1914). Wesley Guard was three times Vice-President of the WM Conference in Ireland (1893, 1902 and 1911).