Marcus Aponius Saturninus was a Senator of Imperial Rome who was the child of wealthy senatorial parents, who owned property in Egypt. He is mentioned in the Acta Arvalia in the year 57; classicist Ronald Syme suggests that he was made a member of the Arval Brethren due to the influence of Annaeus Seneca. Saturninus is mentioned 66 as being present for sacrifices on the Capitol with the emperor Nero. Tacitus calls him a consul, but the date of his office is uncertain. He may have been consul in 55; Paul Gallivan has argued that Saturninus was suffect consul between 63 and 66, by which time he was recorded as becoming promagister.
We hear of him as serving as the governor of Moesia in 69, which may have been an appointment of Galba. He repulsed the Sarmatians, who had invaded the province, and was in consequence rewarded by a triumphal statue at the commencement of Otho's reign.
In the struggle between Vitellius and Vespasian during the Year of the Four Emperors, Saturninus first espoused the cause of Vitellius, with his relation Gaius Dillius Aponianus, and reported on the fomenting rebellion in a letter to Vitellius. He seemed to only stick with Vitellius while this was a safe bet, however, and afterwards declared himself in favor of Vespasian, and crossed the Alps to join Marcus Antonius Primus in northern Italy. Saturninus decided to use the confusion of the shifting loyalties of the legions and tried to have killed the well-liked Tettius Julianus, a partisan of Vespasian in his legion, and brother-in-law of Vespasian's finance minister, on the pretext that Tettius was actually a secret Vitellius supporter. Primus, who was anxious to obtain the supreme command, excited a mutiny of the soldiers against Saturninus, who had after all attempted to assassinate pro-Vespasian factions in his legion. Saturninus was compelled to fly from the camp.