In 1937, during the later stages of the Spanish Civil War, Bastico replaced Mario Roatta as the commander-in-chief of the Italian volunteer corps in Spain, the Corpo Truppe Volontarie.
I 1937 under de senere faser af den Spanske Borgerkrig erstattede Bastico Mario Roatta som øverstkommanderende for det italienske korps af frivillige (Corpo Truppe Volontarie, eller CTV) i Spanien.