He was born at Marykirk, Kincardineshire, on 12 May 1826. He was the son of Alexander Roberts, a flax-spinner. He was educated at the grammar school and Bang's College, Old Aberdeen, where he graduated M.A. in March 1847, being the Simpson Greek prizeman.
He was presbyterian minister (1852-71) in Scotland and London. In 1864, being then minister at Carlton Hill, London, he was made D.D. of Edinburgh. He was also minister at St. John's Wood, and was a member of the New Testament revision company (1870-84). In 1872, he succeeded John Campbell Shairp in the chair of humanity at St. Andrews ; he was made emeritus professor in 1899. He died at St. Andrews, Mitcham Park, Surrey, on 8 March 1901.
He married on 2 December 1852 Mary Anne Speid (died 18 Jan, 1911), and had fourteen children, of whom four sons and eight daughters survived him Roberts co-operated with Sir James Donaldson as editor and part translator of the English versions of ecclesiastical writers published as the 'Ante-Nicene Christian Library' (1867-72, 24 vols.); he translated also the 'Works of Sulpitius Severus' (1895) in the 'Select Library of Nicene and Post-Nicene Fathers.' He is best known for the series of works in which he maintains that Greek was the habitual speech of our Lord, a conclusion which has not met with general favour, despite the ability with which Roberts managed his case.
He was co-editor of the first major edition of the Ante-Nicene Fathers.
