The United Presbyterian Church, formed in 1847 by the union of the United Secession and Relief Churches, inherited from its Secession part missions in the West Indies (see also MS.8020) and in Calabar, Nigeria; soon after the union it took over the work in Jamaica of the Scottish Missionary Society (see MSS.8014, 8984-5) and that in Kaffraria of the Glasgow South African Missionary Society. Missions were later established in Rajputana (1860), Manchuria (1872), and Japan (1873). In addition to foreign missions in the strict sense, the United Presbyterian Foreign Mission Committee was for a long period concerned with Colonial and Jewish mission work, the former especially in Canada, the latter in various centres in Europe (especially Spain) and North Africa, and also with contacts with evangelical churches in Europe.

No incoming letters to the United Presbyterian Church have survived; those to the United Free Church from former United Presbyterian Church fields have been placed with those from former Free Church fields (MSS.7793-7859).