Abstract This article examines whether the mass killings of people with leftist ideology by the Franco regime can be interpreted as genocide in accordance with the provisions of international law. The present study underscores the influence of religion on the configuration of Francoist criminal policy and provides evidence that allows Francoist repression to be considered as genocide. Individuals with leftist ideologies were presented not only as a political group but also as a religious group with atheist and non-Catholic beliefs. In this sense, the mass political repression conducted by the Franco regime fulfils the objective elements (actus reus) of genocide due to the fact the religious element played a significant role in justifying the annihilation of Republicans. The victims of Francoist repression were in fact selected not only because they belonged to a certain political movement or party but also because they belonged to a certain religious group.