 He was one of the founders of the civic group Movement for the Advancement of the Brotherhood, Integrity, Nationalism and Independence (MABINI) and the Free Legal Assistance Group (FLAG).When Corazon Aquino decided to challenge Ferdinand Marcos in the 1986 Snap Presidential Election, Arroyo served as counsel for Cory Aquino during the snap election.During the first EDSA Revolution, he served as one Aquino's key advisers.