Andrew Watson was born in Scotland in 1834 and emigrated with his parents to Waukesha, Wisconsin. He was later educated at both Princeton and Pittsburgh Theological Seminaries and also attended Jefferson Medical College, Philadelphia for some medical courses. After his ordination in 1861, Andrew Watson applied and was appointed to the UPCNA's Egypt Mission. He served in Alexandria and later Mansurah for the first few years and then was sent to Cairo where he spent the bulk of his career.

During his years of service in Cairo Andrew Watson was professor and later head of the Mission Theological Seminary in Egypt. He also was the Moderator at the General Assembly Meeting in Baltimore in 1890 and in 1897 he published History of the American Mission in Egypt. He was involved in reorganizing the civil and political status and relations of the native Protestant communities in Egypt which led the Sultan of Turkey to officially recognize their legal rights. In 1900 he headed a committee to pioneer the establishment of an American Mission in Sudan and in 1910 he was a delegate to the World Mission Conference at Edinburgh. Andrew Watson died in the field in 1916 and was survived by his wife Margaret McVicker Watson, and his sons Charles and Frederick.