[9] She was elected to the Chamber of Deputies for her province, representing the centrist Radical Civic Union (UCR), in 1995, and in 1997, obtained passage of a bill giving constitutional authority to the international Treaty of Disappeared Persons.

Re-elected to Congress, Carrió earned growing publicity as the chair of the Congressional Committee on Corruption and Money Laundering after 1999, particularly during a series of exchanged accusations in 2001 between herself and Economy Minister Domingo Cavallo.

[11] After the rupture in 2000 of the Alliance for Work, Justice and Education (which the UCR had formed in 1997 with Socialists and the Front for a Country in Solidarity), Carrió turned to the Democratic Socialist Party and other politicians with leftist leanings who were discontented in their parties, and formed an informal front, initially called "Argentinians for a Republic of Equals" (Argentinos por una República de Iguales), ARI.

After losing the election, she worked on securing the Civic Coalition ARI, which went through a major crisis during the 2003–07 Kirchner presidency, with members unable to settle their differences and several deputies leaving for the National Government.

She returned to the Lower House of Congress in 2005, after winning a seat as a National Deputy for the Autonomous City of Buenos Aires with just over 20% of votes.

[13] Together with her running mate Rubén Giustiniani (chairman of the Socialist Party), Carrió obtained about 23% of the vote, coming in a distant second after first lady Cristina Fernández de Kirchner.

[citation needed] Carrió joined the Broad Front UNEN alliance upon its formation in June 2013, and was reelected to the Lower House on their ticket in elections that October.

[21] Carrió always appears in public wearing a crucifix, claims to take communion every day and once told Raúl Alfonsín she had seen the Virgin Mary.

Carrió marked her firm stance against abortion before and after entering Congress, including during the time Cambiemos co-founder Mauricio Macri encouraged legislators of the alliance to maturely and responsibly debate an issue, as it divided both the opposition and the ruling party.