Unger's engagement in Brazilian politics began in the late 1970s as Brazil started to democratize. In 1979, he presented himself to the main opposition party, the Brazilian Democratic Movement (MDB), and was appointed chief of staff by party leader Ulysses Guimaraes. His initial work was to develop the positions of the party and draft policy proposals for their party's congressional representatives. When the military regime dissolved the two-party system and established a multi-party system later that year, Unger worked to unite progressive liberals and the independent, non-communist left into the Brazilian Democratic Movement Party (PMDB). As a co-founder of the party, he authored its first manifesto. Unger left the party after the rise of a conservative faction, which was a part of the MDB but had been excluded from the initial formation of the PMDB.