Following his graduation from Union Theological Seminary and his subsequent ordination to the ministry of the Presbyterian Church in the USA, Henry Harris Jessup was appointed as a missionary to Syria in 1855 by the American Board of Commissioners for Foreign Missions. In 1870, when the Syria Mission was transferred from the ABCFM to the Presbyterian Board of Foreign Missions, he thereafter served the latter. Until 1860, Jessup resided in Tripoli with his family, but spent the remainder of his missionary service in Beirut where for thirty years he was acting pastor of the Syrian Church of Beirut and superintendent of its school. He also served as secretary of the Asfuriyeh Hospital for the Insane from its establishment and as a missionary editor of the Arabic Journal, El Nesrah. In 1866, Jessup helped found the Syrian Protestant College, now the American University of Beirut. Besides serving as moderator of the 1879 General Assembly, Jessup authored several works about his mission experience in Syria. He died in service and was buried in Beirut.