Barclay was born near
Strabane in
County Tyrone, Ireland, his family being of
Scottish extraction. He was educated at
Trinity College Dublin, and proceeded B.A. in 1854 and M.A. in 1857, but showed no particular powers of application or study. In 1854 he was ordained to a
curacy at
Bagnelstown,
County Carlow, and on taking up his residence there began to show very great interest in the work of the
London Society for promoting Christianity among the Jews. The question of
Jewish conversion was at that time agitating the religious world in England, and Barclay supported the cause in his own neighbourhood with great activity, till in 1858 he offered himself to the London Society as a missionary. He left Ireland, and after a few months' study in London, was appointed to
Constantinople. The mission there had been established in 1835, but no impression had been made on the 60,000 Jews calculated to inhabit the town. Barclay stayed in Constantinople till 1861, making missionary journeys to the
Danubian provinces,
Rhodes, and other nearer districts. He married Lucy Agnes Tryphosa Andrew (d. 1882), 3rd daughter of Rev. William Wayte Andrew (1804–1889), of Wood Hall, Hethersett, Norfolk, 52 years Vicar of Ketteringham in Norfolk, as is recorded on the latter's mural monument in Ketteringham Church. ==Career in the Anglican Church==