After the rise to power of the fascists, he joined, unlike many other liberals, the democratic opposition around old leader Giovanni Giolitti and in 1924 refused to candidate himself in the fascist-led national union list.
In July 1943, with the Mussolini regime having been overthrown, he was appointed podestà of Turin, but had to resign after 45 days because of the German occupation.
In the liberated Northern Italy in 1945, he became a member of the Consulta Nazionale and in 1946 was elected to the Assemblea Costituente.
Villabruna tried to convince the left-wing dissident group Movimento Liberale Indipendente (MLI) led by Count Nicolò Carandini to return into the ranks of PLI, which they had left in early 1948, but only in late 1951 did this operation come to a successful conclusion.
In 1954 Villabruna became Minister of Industry and Trade in the Scelba government, and let the leadership of the Liberal Party to Giovanni Malagodi, with whom he came into serious quarrels few time later.