The most recent of the Pontifical Mission Societies was founded by Fr. Paolo Manna in 1917 in Italy. Fr. Manna began by encouraging those already engaged in the work of the Church to support the work of the missions and to perhaps become missionaries themselves. To this end, he founded the Missionary Union of Clergy to raise enthusiasm among priests to promote awareness of the missions and to encourage prayer for them. It was hoped that these leaders within the Church (the clergy) would inspire the laity to pray for the success of evangelization, and to spread of the Good News throughout the World.
In 1956, Pope Pius XII included the Missionary Union as one of the Pontifical Missions.