Following two Conferences, the first one held in Hertenstein (municipality of Weggis near Zürich in Switzerland), gathering 78 representatives of federalist movements from 16 European countries in September 1946, and the second one in Luxembourg in October of the same year, these groups, who shared the common belief that only a European Federation based on the idea of unity in diversity could prevent a repetition of the suffering and destruction of the two world wars, so they adopted a declaration-programme which was based on this idea.

Federalists believed that only a common effort of European citizens working towards this goal could create a peaceful and democratic Europe guaranteeing freedom and the protection of human rights.

The foundation of the UEF followed the two Conference of Hertenstein (municipality of Weggis near Zürich in Switzerland), gathering 78 representatives of federalist movements from 16 European countries in September 1946, and in Luxembourg in October the same year.

Federalists believed that only a common effort of European citizens working towards this goal could create a peaceful and democratic Europe guaranteeing freedom and the protection of human rights.

At a second meeting in Luxembourg these groups agreed on establishing a permanent European secretariat in Paris and another one in New York City for global federalists.

But it was in Paris, on 15 and 16 December 1946 that UEF was officially brought into life, its function being to co-ordinate and intensify the activities of the different movements and to organise them into a federal structure.

The motions adopted defined the principles of fédéralisme to which the organisation adhered and its objectives for European unification.

Among the association's first leaders were Alexandre Marc, Denis de Rougemont, Altiero Spinelli, Henri Frenay.

The fundamental tool was a petition, signed by thousands of citizens across Europe and a large number of eminent people in political, intellectual and scientific life, which asked the Advisory Assembly to draw up a text for a federal pact, and recommend its ratification to the member states of the Council of Europe.

An important part of the history of UEF was the Campaign for the Federal European Constitution in Nice in which 10,000 people, including hundreds of local administrators, participated.[when?

Constituent organisations are free to take up any activities within the general political framework of UEF at the European level.