In the spring of 44 BC Cassius Parmensis participated in the assassination of Caesar by members of the Senate. In 43 BC, following the murder, he became a "quaestor" and built a fleet which supported Gaius Cassius Longinus against Publius Cornelius Dolabella off the coast of the province of Asia. At the same time he wrote a report to Cicero from Cyprus on the situation, which has been handed down in the latter's correspondence.