Arcos met Fidel Castro at the University and later, participated in the failed 1953 attack on the Moncada army barracks, where he was shot and left partially paralyzed.

Arcos was sentenced to 10 years in prison, but was released by a general amnesty in 1955. After a brief exile in Costa Rica, he joined the rest of the movement in Mexico. Due to his paralysis, Arcos was unable to participate in the Granma expedition to Cuba, but instead remained in Mexico as chief of the 26 of July Movment. A few days later, his brother, Luis Arcos Bergnes, who left with the expedition, was killed by Batista's forces as the Granma landed.

Known by the pseudonym of "Ulises," Arcos traveled throughout Costa Rica, Venezuela, and the United States gathering munitions for the 26 of July Movement and also established a clandestine radio named "Indio Apache" from Mexico. After the Cuban Revolution in 1959, Arcos returned to Cuba and was appointed by Castro as Cuba's Ambassador to Belgium. Arcos continued as Ambassador until 1964, when he began to question the authoritarian nature of the Cuban regime. That year, he returned to Cuba.

In 1965, he was offered a new post within the government, but wished to remain in the foreign service. Raul Castro offered him a post in Moscow but Arcos refused. Finally, he was told he would be sent to Italy. However, notification never arrived. Several months later, on March 15, 1966, he was detained. In 1967, he was sentenced to 10 years imprisonment for alleged "counter-revolutionary activity." He was released after serving three years of the sentence, and upon release applied for permission to leave the country, which was refused by the Cuban government.

In 1981, both Gustavo and his brother Sebastian, were charged with attempting to leave the country illegally. Imprisoned once again, Arcos began to communicate with other political prisoners. Some had been jailed in the early 1960's as "counter-revolutionaries," while others had been jailed later as "microfactionaries," a grouping of socialists who protested the Revolution's authoritarian characterisitcs. By 1983, Gustavo joined them as they formed the Cuban Committee for Human Rights from prison.

Soon thereafter, the Committee began to send out proclamations denouncing the deplorable conditions in which political prisoners were kept. By 1986, due to international pressure, the Cuban government was forced to allow a few concessionssuch as visits by several international human rights organizations and the release of several prisoners, who then extended the work of the Committee to the streets of Havana. In March 1988, Arcos was released from prison, and several months later became executive director of the Committee, replacing Ricardo Bofill, who had been forced into exile by the Castro regime.

Arcos continued the work of the Human Rights Committee, informing the Cuban people of the Universal Declaration of Human Rights and communicating to the international community the list of gross violations of human rights committed daily by the Castro regime against Cuban citizens.

In 1990, against the protests of many exiled Cuban activists, Arcos issued a statement to Castro asking him to convene a "National Dialogue," which would include all segments of Cuban society, on the island and in exile. During his address to the Worker's Congress on January 28, 1990, Castro issued his response noting that "the Cuban people" will take care of those activists. By March 5, goverment sponsored mobs attacked Sebastian Arcos' house. On March 8, another mob, led by future Foregin Minister Roberto Robaina, attacked Gustavo's home.

From exile, many old friends asked Gustavo to dissolve the Committee to save the activists' lives. Gustavo replied,"The Cuban Committee for Human Rights will continue its work, even if it costs us our own lives...no terror, nor propaganda will be able to deter the development of humanistic ideas in our country." Dissenting Voices Vol.1 No.1 May 19, 1995
International Republican Institute