With Juan Garcia Oliver and Buenaventura Durruti, Ascaso helped establish the Solidarios group in 1919. Two years later members of the group were involved in the murder of Eduardo Dato, the Spanish prime minister.
In 1923 the group assassinated Juan Soldevila Romero, the Archbishop of Sargossa, in revenge for the murder by the police of Salvador Segui, a CNT leader.
Ascaso and Buenaventura Durruti fled to France in June 1923. In protest against the dictatorship of Miguel Primo de Rivera, Durruti took part in the border raid at Vera del Bidosa on 6th November, 1924.