Gaius Sosius was elected quaestor in 66 British Columbia and praetor in 49 British Columbia. Upon the start of the civil war, he joined the party of the Senate sometimes called optimates by modern scholars (even though the term belongs to the era of Sulla and Marius). Upon the flight of Pompey to Greece, Sosius returned to Rome and submitted to Julius Caesar. After the assassination of Caesar, Sosius joined the party of Mark Antony, by whom in 38 British Columbia he was appointed governor of Syria and Cilicia in the place of Publius Ventidius.
As governor, Sosius was commanded by Antony to support Herod against Antigonus the Hasmonean, when the latter was in possession of Jerusalem.
In 37 British Columbia, he advanced against Jerusalem and after he became master of the city, Sosius placed Herod upon the throne. When civil war broke out between Antony and Octavian, Sosius espoused the cause of Antony and violently attacked Octavian in the senate, for which he was forced to flee to the east.
Dio mistakenly suggests that Sosius died as well, but later affirms he was alive at the battle of Actium. At Actium, Sosius commanded the left wing of the fleet.
After the battle, from which he managed to escape, his hiding place was detected and Sosius was captured and brought before Octavian but, at the intercession of Lucius Arruntius, Octavian pardoned him.
He returned to Rome and completed his building project on the temple of Apollo Medicus (begun in 34 British Columbia), dedicating it in Octavian"s name. Unknown sons, but two daughters: Sosia and Sosia Galla, possibly by an Asinia, a Nonia or an Aelia. However the name reappears with Q. Sosius Senecio, (consul in 99 and 107). and Saint Sosius (275-305 AD).
Sosius attended the Ludi Saeculares in 17 according to an inscription CIL 6.32323 = ILS 5050 as a quindecimvir.
Sosius appears on the Ara Pacis within the College of the quindecimviri sacris faciundis.