Gaius Trebonius was a Roman politician and general. As a patrician, he showed conservative tendencies during his term as quaestor beginning in 60 B.C., but he later became a strong supporter of Julius Caesar and the populares.
As tribune, in 55 B.C. he sponsored the Lex Trebonia, by which Pompey and Crassus, that year's consuls, were assigned, respectively, the provinces of Spain and Syria and by which the assignment to Caesar of Gaul and Illyricum was extended. Although Cicero was persuaded to support the law favoring the dynasts, Cato regarded these extraordinary powers as foreshadowing the end of the republic.
During the second civil war beginning in 49 B.C. Trebonius commanded three legions under Caesar, whose protege he became and under whom he was appointed praetor in 48 B.C., and propraetor of Spain in 47 B.C.; although he was driven from Spain by the revolt of his troops, he became consul in 45 B.C. Despite promises of additional favors, Trebonius joined the conspiracy against his patron, delaying Mark Antony's entrance into the Senate while Caesar was murdered in 44 B.C.
In the following year Trebonius was made proconsul of Asia, a post which Caesar had promised him before his death. He was murdered, supposedly at Smyrna, by Publius Cornelius Dolabella, governor of Syria, after he had been in office only a short time in 43 B.C.