He won 247,500 votes (13.10%) in the 1996 elections for Head of Government of the City of Buenos Aires, and five members of his party became part of the Constituent Assembly.

For the 2000 elections for the head of government of the Autonomous City of Buenos Aires, he formed an alliance with Action for the Republic, the party of former minister of the economy Domingo Felipe Cavallo, running as the candidate for deputy head of government for the Encounter for the City coalition, which came second in the election, winning more than 33% of the votes and seats for 20 of its legislators.

Following Kirchner's victory in the 2003 presidential elections, Beliz became Minister of Justice, Citizen Security, and Human Rights and launched a campaign to promote transparency within Argentina's federal judiciary.

He advocated for the impeachment of members of the Supreme Court who were suspected of corruption and instituted the method of self-limitation in the appointment of judges by the Office of the President through a system of challenges and public hearings, which allowed for greater transparency and citizen participation.

[6] As Secretary of Strategic Affairs, he is a cabinet minister and is responsible for designing and implementing the foreign relations strategy for the Office of the President, working in partnership with Argentina's other ministries.

[7] His work also involves planning and evaluating strategic affairs, international and institutional public policies, and Argentina's financial relationships with multilateral organizations.

He also coordinates the analysis, planning, monitoring, and continuous evaluation of matters that relate to Argentina's foreign policy and national security strategy.