As secretary of the National Fascist Party (PNF), he created the Ceka, a secret police organization established on the model of the Soviet Cheka.

[1] Tried as instigator of the murder of Matteotti in November 1925, Marinelli was defended by Roberto Farinacci, and eventually sentenced to a light punishment.

He remained out of the spotlight during most of the next two decades of Fascist rule, and appears to have been involved in the crushing of internal opposition to Mussolini (including moves inside the PNF).

[1] As a member of the Grand Council of Fascism, he joined the on 25 July 1943 coup d'état carried out by Dino Grandi against Mussolini in an attempt to make the Kingdom of Italy switch sides from the Axis powers to the Allies during World War II.

When Nazi Germany helped Mussolini re-establish his rule as leader of the Italian Social Republic in northern Italy, Marinelli was convicted of treason during the Verona trial of 1944, and executed by firing squad along with former minister of foreign affairs Galeazzo Ciano, Emilio De Bono, Carlo Pareschi, and Luciano Gottardi.