Presbyterian work in Mesopotamia dates from 1834 when the American Board of Commissioners for Foreign Missions sent the Reverend and Mrs. Justin Perkins to labor among the Nestorian Christians. During the next 30 years, individual missionaries ministered to this group and to the Kurds in the mountainous areas between Urumia and Mosul. In 1870, the Board of Foreign Missions (PCUSA) assumed the work of the American Board in the areas of Urumia and Tabriz and organized the West Persia Mission. By 1891, the American Board's work in Mosul had been transferred to the PCUSA. In 1900, this work was again transferred, to the English Church Missionary Society under the Church of England.
The upheaval resulting from the First World War precluded the Church Missionary Society from resuming its pre-war responsibilities. Short of a complete withdrawal from the field, the only viable alternative was to transfer this work to the various American Mission groups that had been operative there prior to 1900. Hence, out of the problems of adjustment, reorganization and depleted staffs arose the idea of a United Mission in Mesopotamia. Initially, the plan was to include all of the Presbyterian/Reformed Churches in one mission. However, the plan as actually adopted in 1924 included the PCUSA, the Reformed Church in America and the Reformed Church in the United States. In 1935, the name of the mission was changed to the United Mission in Iraq. Following denominational reorganizations in the 1950s and 1960s, the Reformed Church in America, the PCUS, the United Church of Christ and the UPCUSA constituted the Mission. The Mission was governed through a Joint Committee headquartered in New York.
The work of the United Mission centered around five stations, three of which were staffed by Presbyterian personnel. These included Mosul, the center of the old West Persia Mission; Hillah, occupied as an outstation in 1926 and elevated to full station status in 1930; and Dohuk, occupied in 1930. Work in Baghdad was directed by the Reformed Church in America, while the Reformed Church in the United States operated Kurkuk. The primary focus of the Mission's work was educational, with schools being established in Baghdad and Mosul.
By the early 1960s, all of the evangelical forces operating in Iraq were part of the United Mission, though an indigenous national church did not yet exist. Early in 1970, the Mission's two schools were seized by the Iraqi government, causing the Joint Committee to suspend indefinitely all of its activities in Iraq. Effective 30 June 1970, the United Mission in Iraq and its governing body were formally dissolved.