In 1959, a year after the election of Carvalho Pinto, Arruda Sampaio became coordinator of the government's action plan, a position he held until 1962.

In 1970, he moved to the United States, where he worked at the FAO and at the IDB in Washington, before beginning a master's degree in agricultural economics at Cornell University.

Returning to Brazil in 1976, he began teaching at the Getulio Vargas Foundation, where he founded the Center for Contemporary Cultural Studies (Cedec) and engaged in the campaign to end the military regime and the amnesty of politicians who had been expelled from political life.

Alongside Almino Affonso, Francisco Weffort and Fernando Henrique Cardoso, the party nurtured important leaders like Marcos Freire and Jarbas Vasconcelos.

As a member of the constituent assembly, he became widely known for proposing and defending a model of constitutional reform which aimed to wipe out the plantations, and also became the only PT deputy to chair a working committee.

After leaving the Workers Party, in which he was a founding member and historic leader, Arruda Sampaio joined the PSOL.

During the Second Congress of the PSOL, the state deputy Raul Marcelo launched the pre-candidacy of Arruda Sampaio to the presidency.

His purpose was to build a program that served to counter the effects of the economic crisis on workers, and the unity of the socialist left against capital.