The UDB was essentially a "labourist" (travailliste) party (which would now be placed on the centre-left) and was much keener on secularisation (déconfessionnalisation) and progress (progressisme) than the PSC-CVP, wishing to bring those of all philosophical and religious persuasions under one flag.
It had ambitions to be a nationwide party, but was mainly restricted to Wallonia and the French-speakers in Brussels, making it short on influence in the capital's political circles.
Its leaders came from the Belgian resistance and the other parties hoped that the UDB and CVP would compete against and weaken each other by splitting the Christian vote.
When the PSC-CVP refused to participate in the second government of Achiel Van Acker (2 August 1945 - 9 January 1946), two UDB members of parliament joined it - Marcel Gregoire for Justice and Jacques Basyn for Defence.
UDB hopes were high at the general elections on 17 February 1946, but these were disappointed, with the party only gaining 51,095 votes (mainly in Brussels) and only managed to elect one person to the Chamber of Representatives (Paul M. G. Lévy for the arrondissement of Nijvel, though he resigned after only a few weeks and was replaced by Werner Marchand).