Aquino is a leading member of the Liberal Party. He currently holds the position of Vice Chairman of the Liberal Party, having assumed the post on 17 March 2006. He was previously Secretary General of the party (1999-2002), Vice-President of the Luzon Liberal Party (2002-2004), and Secretary General of the party (2004-16 March 2006).
Aquino is associated with a faction of the Liberal Party which opposes the government of President Gloria Macapagal-Arroyo, citing alleged human rights violations.
Aquino was elected to the House of Representatives in 1998, representing the 2nd District of Tarlac. He won re-election in 2001 and 2004, and served until 2007.
Aquino served on numerous committees as a member of Congress:
Barred by term limits from seeking a fourth term as the Representative for the second district of Tarlac province, Aquino was elected to the Senate in the May 14, 2007 midterm elections under the banner of the Genuine Opposition (GO), a coalition comprising a number of parties, including his own Liberal Party, seeking to curb attempts by President Gloria Macapagal-Arroyo to amend the Constitution. In his political ads, he was endorsed by younger sister, TV host Kris Aquino, and mother, the late former President Corazon