He joined the local socialist movement, then growing in his region, and attended various conferences of a political nature[3] together with his friend, the young Benito Mussolini.
In the same year he was secretary of the XIV national congress of the PSI held in Ancona at the end of April and major player in the Red Week strikes in June.
[6][7] A few months later he took over the sole direction of the socialist newspaper from Forlì La Lotta di Classe[3] of which he had already been co-director since 1912 to replace Mussolini, who had moved on to Avanti!.
[9][1] After the war ended with 1918, Vernocchi was placed on leave by the Royal Italian Army on 5 June 1919[7] and moved to Rome, where he began his important collaboration as editor with Avanti!, the party newspaper.
[6][3] In addition to his work as editor for the newspaper, Vernocchi began to participate with increasing commitment in the Roman Union of the PSI, of which he was the leader until the fascist government dissolved political parties.
[7] In fact, in 1926, with the promulgation of the exceptional laws, the PSI was dissolved and Vernocchi was subjected to a strict surveillance regime after his failed attempt to leave the country in 1927.
[6][3][1] On 22 July 1942 it was in his studio in Rome that the meeting was held in which the refoundation of the party was decided; Oreste Lizzadri, Giuseppe Romita, Nicola Perotti and Emilio Canevari also took part.
[6][3] The party began to consolidate: the "group of five" re-established contacts with the old militants, traveling throughout central and southern Italy and promoting anti-fascist actions directly in the city of Rome: distribution of leaflets and clandestine press and support for strikes (particularly important was the one on 1 May 1943 led by university students).
[14] The following year Vernocchi and Romita were able to go, representing the PSI in the Opposition Committee, to King Vittorio Emanuele III to ask for the dissolution of the National Fascist Party.
Jointly directed by Vernocchi, the Christian Democrat Alberto Canaletti Gaudenti and the communist Mario Alicata, it was an expression of the interconfederal union committee, a sign of the major anti-fascist parties’ wish to unite their forces.
The following month, continuing the activity of the Constituent Assembly, he was the rapporteur of the draft law n.12 concerning "Regulation of the national film industry", presented by De Gasperi and several of his ministers.