Born in , Loures, Lisbon District, Jerónimo de Sousa was born into a humble working-class family, dominated by the right-leaning regime of António de Oliveira Salazar.
After the replacement of Salazar by Marcello Caetano in 1969, the regime made some slight democratic openings, one of them was the possibility of workers without any record of illegal political activity participate in the elections for the respective Unions.