Reverend Barclay was born in Glasgow. He graduated from the University of Glasgow and Free Church College, Glasgow. He was inspired by Reverend Carstairs Douglas and to be a missionary to Formosa. He arrived in Taiwan in 1875, started his service including teaching in the Tainan Theological College, established the first printed newspaper “Taiwan Church News” printed using the Peh-oe-ji (白話字）romanization, and edited the dictionary “Supplement to Dictionary of the vernacular or spoken language of Amoy”. He rested in peace in 1935 and was buried in Tainan.