Comrades often referred to Santucho by his nickname "Roby," although he was known to use other noms de guerre: Miguel, Comandante Carlos Ramírez, and Enrique Orozco, among others.

Santucho was instrumental in early efforts to unite the Frente Revolucionario Indoamericano (FRIP), of which he was then leader, with the Trotskyite organization Palabra Obrera.

On Santucho's initiative, and following shortly after the popular upheaval of 1969 known as "the Cordobazo", the Fifth Congress of the PRT voted in 1970 in favor of the formation of the People's Revolutionary Army (ERP).

In Chile, Santucho and his companions were granted safe passage by then president Salvador Allende to continue onwards to La Habana, Cuba.

Santucho would later resist pressures to abandon the armed struggle and enter into dialogue with President Héctor Jóse Cámpora, the Peronist figurehead for then-exiled Juan Domingo Perón.

In a series of public statements he denounced the counterrevolutionary character of the Campora government, as well as Perón's conciliatory attitude towards the Argentine business class and far right.

According to surviving member and later secretary general of PRT-ERP Arnol Kremer (pseudonym Luis Mattini), the ERP and Montoneros leadership were coordinating efforts to build a unified guerrilla force shortly before Santucho's death.

Regarding Peronism, Santucho considered the phenomenon a prime example of "Bonapartism", wherein a strongman figure mediates between competing class interests for the purpose of guaranteeing "national unity".

In that sense, Santucho was equally opposed to a populist movement such as the Montonero's as he was to the gradualist platform of the Communist Party, advocating instead for a socialist revolution as the only viable option for national liberation.