The National Democratic Union (, UDN) was a political party that existed in Brazil between 1945 and 1965. It was ideologically aligned with conservatism. During most of its existence, it was the country's second-strongest party. This constant opposition to Vargas was the party's main characteristic. Although Quadros was not a UDN member himself, most of the ministers in the Quadros Cabinet were members of UDN. The party was soon dissatisfied with Quadros, who resigned in a clumsy political maneuver. Without UDN's support, Quadros lost the majority of seats in the Congress, and soon found out it was impossible to govern without the backing of the Parliament. Goulart's reforms alienated some members of the moderate PSD, leading to withdrawal of its support to the Goulart government in the National Congress, thus leaving the President in a complicated situation. In April 1964, Goulart was deposed by 1964 Brazilian coup d'état, which had the support of many UDN members.
Ideology
Even before UDN supported the 1964 Brazilian Coup d'état, opponents of UDN characterized it as a golpista (pro-coups d'état) party. However, the party was not conservative as a whole. Liberal and authoritarian, conservative and progressive theses coexisted in UDN. Contesting the results whenever losing an election was also a common practice inside UDN. and the aspirations of urban middle classes, all of which became unofficially known as "udenismo".
- 1955–1957: Milton Campos
- 1957–1959: Juracy Magalhães
- 1959–1961: José de Magalhães Pinto
- 1961–1963: Herbert Levy
- 1963–1965: Olavo Bilac Pinto
- 1965: Ernani Sátiro
Secretaries-General
- 1945–1947: Virgílio de Melo Franco
- 1947–1949: Aliomar Baleeiro
- 1949–1951: José Monteiro de Castro
- 1951–1953: Rui Santos
- 1953–1955: Virgílio Távora
- 1955–1957: João Agripino Filho
- 1957–1959: Guilherme Machado
- 1959–1961: Aluízio Alves
- 1961–1963: Ernani Sátiro
- 1963–1965: Rui Santos
- 1965: Oscar Dias Correia