Vibius Julius was the third son of Flavius Julius, younger brother of Quintus Julius and Lucius Julius, and was of the influential House of Julii of the Roman Republic. Vibius Julius was a skilled bureaucrat with an understanding of mathematics, and he was also a confident commander. In 270 BC he assisted his father in capturing Segesta from the Ligurians. He later took command of an army of Roman troops and invaded Gaul, capturing Massilia in 258 BC and campaigning against the Gauls in southern France. In 255 BC, he conquered Narbo Martius after victories at Arelate and Nemausus, and he expanded Roman rule to the Pyrenees.