She was also the founder and leader of Partido Revolucionário do Proletariado (PRP), a political organization never formalized as a party and created to support the BR.
Maria Isabel Augusta Cortes do Carmo was born in Barreiro, on the left bank of the River Tagus to the southeast of the Portuguese capital of Lisbon, on 12 September 1940.
After receiving a PhD from the same faculty, she practised medicine as an assistant physician at the Hospital de Santa Maria in the north of Lisbon.
At this time, after the 1968 Warsaw Pact invasion of Czechoslovakia made her disenchanted with the Soviet Union, and becoming frustrated with the PCP's unwillingness to carry out armed activities, Carmo founded, with Carlos Antunes and Pedro Goulart, the Brigadas Revolucionárias/Revolutionary Brigades (BR).
On December 31, 1972, the BR infiltrated the vigil of Capela do Rato, a protest organised by a group of Catholics who took a stand against the colonial war.
The PRP's main objective was to broaden the base of support and provide political protection for BR terrorist attacks.
Unlike the BR, which, at first, still had some support among progressive Catholics, the PRP established its base among the more-radical far left whose ideology was Revolutionary Socialism.
Later in 1975, during the so-called Hot Summer of political, social and military instability, the country was ruled by a communist government with the support of Operational Command of the Continent (COPCON), led by Otelo Saraiva de Carvalho.
At the same time she said to a weekly newspaper: "Never, anywhere in the world, has socialism been implemented through elections and we believe that through them, the bourgeoisie will never lose its privileges" [14][15] The PRP/BR argued in a manifesto that in order to strengthen the alliance between the people and the Armed Forces Movement, which had initiated the Carnation Revolution, it would be necessary to organize a huge revolutionary army to be formed by the military and members of grassroots organizations (workers, residents, farmers, etc.).
[17][18] The BR became frustrated with the end of the revolutionary period and with the beginning of the consolidation of democracy and the preparation for Portugal's entry into the European Economic Community (EEC), and carried out a series of attacks and bank robberies.
[19] On 10th September 1975, Carmo and Antunes received, from a Copcon official, 1000 machine guns diverted from the General Deposit of War Material, situated near Loures, which were to be used to arm the BR as well as its supporters.
They refused and decided that the BR should split from PRP and go underground to operate clandestinely and keep all weapons including the machine guns.
[19][29][30] In 1978 the bombing of a freight train in Mauritania, which caused the death of eight soldiers, opened a series of internal discussions and disputes inside the Brigadas Revolucionárias.
However, at that time most of the BR leaders, including Isabel do Carmo, were already in prison for bank robberies and denied knowledge of this action.
[30] Previously he had been a member of the Movement of Armed Forces, which had initiated the Carnation Revolution and later he led the far-left attempted coup on 25 November 1975.