Mecilius Hilarianus was a Roman politician and senator in the fourth century AD.
In 316 AD, Hilarianus served as Corrector (Governor) of the province of Lucania et Bruttii in Southern Italia.
[1] In 332 AD, Hilarianus was appointed consul together with Lucius Papius Pacatianus as his colleague.
[2] In 337 AD, after the death of Emperor Constantine I, he supported Constans I in his conflicts against his brothers.
[3] After the death of Constans in 350 AD, he fled to the court of Constantius II, returning to Rome after the latter's victory over Magnentius.