As a youth, Martins was not only a student leader but after the 1964 coup d'état in Brazil, engaged in armed struggle and urban guerrilla. In the communist group MR-8, he was known as "Valdir" (codename). During the military dictatorship, he had a prominent role within the movements which fought against the regime. The acts included bank robbery (then called "revolutionary expropriation" by the guerrilla rhethorics) and assaults on police and military. The amount was used to buy weapons and bribe authorities to release fellow militants. Franklin Martins was held in prison between October and December 1968, being released on the eve of Institutional Act#5, which dissolved the Congress, and institutionalized censorship and torture in Brazil.