[3][4] In 62 BC, having been elected tribune of the plebs, Thermus cooperated with his colleague Cato in forcibly opposing a bill by the praetor Julius Caesar to reassign responsibility for the reconstruction of the Temple of Jupiter Capitolinus to Pompey.
[5] The attempt to overcome Cato and Thermus' veto triggered violent clashes and a senatus consultum ultimum before order was restored to the city.
[7] From 51 to 50 BC, he was prorogued to Asia pro praetore and successfully administered the province, so much that even Cicero sent him letters with his compliments.
[8][9] During Caesar's civil war, still holding imperium,[10] he attempted to defend Iguvium (modern Gubbio) from Caesar's invasion of Italy, but his raw recruits deserted before the Caesarian advance under Curio, forcing him to retreat.
[11][12] In 43 BC he was one of several envoys sent by the Senate to negotiate with Sextus Pompeius in Sicily.