[2][3] During the Third Mithridatic War (73-63 BC) against Mithridates VI of Pontus and Tigranes the Great of Armenia, Celer was a commander of some sort.
TRS Broughton in the Magistrates of the Roman Republic suggests he possibly was a legate, military tribune, or quaestor.
In the winter of 66 BC, Oroeses, king of the Caucasian Albanians attacked Pompey's army during Saturnalia celebrations in Lesser Armenia.
Celer vigorously repulsed Oroeses while Flaccus and Pompey, who were in charge of the other two divisions, defeated the other Albanians.
[17] After Catiline's involvement became clear and he fled Rome, Celer played an important role in the campaign suppressing the conspiracy.
However, the divorce – amid claims of infidelity – harmed the public reputation and dignitas of the Caecilii Metelli: the two brothers of Mucia, Celer and Nepos, took this slight very seriously.
[25] During Celer's consulship, Pompey sought senatorial ratification of his eastern settlements and land grants for his veterans.
Lucius Licinius Lucullus, whom Pompey had replaced in command pursuant to the lex Manilia of 66 BC, challenged his rival's actions: instead of approving Pompey's settlements as a whole, Lucullus stalled the entire process by having each element reviewed in committee before separate votes on each part.
For this strong opposition, the pro-Pompeian plebeian tribune Lucius Flavius had Celer thrown into jail and attempted to keep him there by sitting on a bench before the door.
Celer, intending to stay the night, had his allies cut a hole in the wall so that senators could attend to him.
[29] These victories for Celer, however, saw Pompey join a political alliance with the next year's consul, Gaius Julius Caesar, and Crassus.