Moreau joined the
Radical Civic Union (UCR) in 1960, when he was 14. In 1968, he was one of the founding members of the
Junta Coordinadora Nacional, an inner youth current within the party, and the
Franja Morada, the UCR's student wing. Later, in 1972, he participated in the formation of the Renovation and Change Current, another group within the UCR led by
Raúl Alfonsín.
First terms as deputy In 1983, upon the fall of the
last military dictatorship in Argentina, Moreau
ran for a seat in the
Chamber of Deputies. Upon his election, he served as president of the parliamentary commission on communication and as vice-president of the UCR
bloc. Toward the end of the 1980s, Moreau became leader of the Radical Committee of
Buenos Aires Province. Due to his closeness with then-president Raúl Alfonsín, Moreau was one of the government's spokespeople during the 1987
Carapintadas uprising. From April to June 1989, Moreau was
president of the Chamber of Deputies. He was re-elected to the Chamber in
1987 and
1991. Moreau played a prominent role in the establishment and development of the
National Commission on the Disappearance of Persons (CONADEP), the commission created to investigate the fate of the
desaparecidos (victims of
forced disappearance) and other human rights violations during the dictatorship. In 1995, Moreau was elected to the
National Senate by the
Legislature of Buenos Aires Province, where he became part of the parliamentary commissions on budget and treasury affairs, accords, culture and education. From 1995 to 2001, he was the first vice-president of the Senate. During his time as Senator, Moreau was a staunch opponent of the neoliberal economic policies of President
Carlos Menem.
Presidential run Moreau was the UCR's presidential candidate in the
2003 general election, having won the party's nomination over
Rodolfo Terragno. During the campaign, Moreau apologized to the Argentine society at large for the party's inner strife. The economic crisis, the
December 2001 riots and the subsequent resignation of President
Fernando de la Rúa had all contributed to a considerable loss of support for the party, and on election day, Moreau received merely 2.34% of the popular vote. ==Leader of the MNA==