The United Society for the Propagation of the Gospel (USPG) came into existence on 1 January 1965. It was formed by the merger of the Society for the Propagation of the Gospel in Foreign Parts (SPG) and the Universities' Mission to Central Africa (UMCA). On 1 January 1968 the Cambridge Mission to Delhi (CMD) also joined USPG.

The Society for the Propagation of the Gospel in Foreign Parts (SPG) was the inspiration of the Revd. Dr. Thomas Bray. At the end of the 17th century he visited Maryland on behalf of the Bishop of London and found the Church of England in the American Colonies to be disorganised and with little spiritual vitality. Following his return to England, Dr. Bray obtained a charter from King William III, which was issued on 16 June 1701. The charter established SPG as an organisation able to send priests and schoolteachers to America to help provide the church's ministry to the colonists and to take the message of the gospel to the slaves and native Americans. The Society's first missionaries began work in America in 1702 and, by the time the USA claimed independence, SPG had supported the work of about 300 men (plus a tiny number of school mistresses) and had made a substantial contribution to the foundation of the Episcopal Church.

Soon after 1701 the SPG's horizons began to expand, first to the West Indies and Nova Scotia and later in the 18th century to the rest of Canada, Australia, New Zealand and West Africa. Early in the 19th century SPG began sending missionaries to countries where migrants from Britain and Ireland were not present in large numbers, such as India (1820) and South Africa (1821). Work among indigenous people came to be a higher priority than care of the colonists, although the emphasis on pastoral ministry and education remained. During the second half of the 19th century there were new developments. The Society allowed women, including single women, from Britain and Ireland to be missionaries in their own right, rather than only as the wives of male missionaries. Increasing numbers of indigenous missionaries, both men and women, were supported in their work by the SPG. Medical work came to be recognised as an effective means of Christian ministry, demonstrating God's love for everyone. The Society also began to work in countries outside the British Empire, such as China (1863) and Japan (1873). From this period until the Second World War the pattern of mission work remained similar: pastoral, evangelistic, educational and medical work contributing to the growth of the Anglican Church and aiming to improve the lives of the people.

David Livingstone's return from Africa in 1857 led to the formation of Universities' Mission to Central Africa (UMCA). Following a challenge issued during his lectures in Cambridge and Oxford, the universities prepared to send a mission to central Africa led by a bishop. Charles Mackenzie was consecrated in 1860 and the next year sailed up the Zambezi and Shiré rivers with a small group to start work. Malaria soon took its toll so Mackenzie's successor, Bishop William Tozer, abandoned the area around Lake Nyasa and moved his base to the island of Zanzibar in 1864. Establishing the Mission's work and opposing the East African slave trade were the initial priorities. UMCA's return to Lake Nyasa came later, this time overland via mission stations established on mainland Africa (now Tanzania) during the late 1870s and early 1880s. Two missionaries, Charles Janson and William Percival Johnson, finally reached the Lake in 1884. For the next 25 years UMCA's work developed in Zanzibar, Tanganyika, Nyasaland (now Malawi) and the north of Portuguese East Africa (Mozambique), but spread no further geographically until 1910 when the Mission began work in Northern Rhodesia (Zambia).

UMCA aimed to establish the church in Central Africa and both men and women were involved from its earliest days in contributing to making this a reality. Evangelistic, pastoral and educational work were all carried out by both Africans and Europeans. Medical work soon became an important addition and one of UMCA's major contributions in this sphere was its participation in the fight against leprosy.

The Cambridge Mission to Delhi (CMD) was one of a number of missions launched from universities in Britain and Ireland. The Cambridge theologian BF Westcott's vision of a serious and respectful engagement with Indian religious tradition led to CMD's formation in 1877. Much of its work was done through two religious communities: the Brotherhood of the Ascension, a community for men, and St Stephen's Community for women. St Stephen's Hospital and St Stephen's College became important institutions in both city and nation; the latter providing an example of inspired Indian leadership supportive of Indian nationalism through the work of S.K. Rudra, principal from 1906-1923. The most striking innovation since joining USPG has been the Brotherhood's bold mission of service among the most disadvantaged in the rapidly growing city.

Following the Second World War and, more significantly, India's independence in 1947, the mission agencies were challenged by a rapidly changing world. SPG celebrated its 250th anniversary in 1951 and UMCA its centenary in 1957 in the context of decolonization, newly autonomous churches developing their own lives, and the beginning of a gradual decline of interest in mission in the church in Britain and Ireland. However, new concepts of mission were developing which emphasised the interdependence of the world church and the sharing by all in its life. Authority and influence were no longer to be held solely by the mission agencies but replaced by relationships of equal partners. This changing world and church brought SPG and UMCA in the early 1960s to consider their connection and the result was the decision to merge.

USPG's role since 1965 has been to facilitate the movement of people, resources and ideas around the world church. Missionaries leave their home countries to share their lives and skills. USPG transfers funds to enable the work of the church and provides opportunities for church workers to spend time in training or study either at the Society's United College of the Ascension in Birmingham, or at other institutions worldwide.

Since 1701 the Society has supported around 15,000 men and women as missionaries in many parts of the world. Together with the financial resources and training opportunities made available by the Society, USPG and its missionaries have made a major contribution to the growth and life of the Anglican Church in the 300 years of the Society's existence.