Little is known about Philip's early life and political career. He was born in Damascus in the Syria Roman province, son of a Julius Marinus, a local Roman citizen, possibly of some importance. The name of his mother is unknown, but sources refer to a brother, Gaius Julius Priscus, a member of the Praetorian guard under Gordian III. Philip married Marcia Otacilia Severa and had a son named Marcus Julius Severus Philippus in 238.
In 243, during Gordian's campaign against the Persians, the Praetorian prefect Timesitheus died under unclear circumstances. At the suggestion of his brother Priscus, Philip became the new Praetorian prefect, with the intention that the two brothers would control the young emperor and rule the Roman world as unofficial regents. Following a military defeat, Gordian was killed by mutinous soldiers somewhere near the Euphrates river. Philip is universally held directly responsible for this mutiny, especially as he was proclaimed emperor after Gordian's death. Philip was not willing to repeat the mistakes of previous usurpers, and was aware that he had to return to Rome in order to secure his position with the senate. He thus traveled west, after concluding a peace treaty with king Shapur I of Persia, and left his bother Priscus as extraordinary ruler of the Eastern provinces. In Rome he was confirmed emperor, and nominated his young son Caesar and heir.
Philip's rule started with yet another Germanic incursion on the provinces of Pannonia and the Goths invaded Moesia (modern-day Bulgaria) in the Danube frontier. They were finally defeated in 248, but the legions were not satisfied with the result, probably due to a low share of the plunder, if any. Rebellion soon arose and Tiberius Claudius Pacatianus was proclaimed emperor by the troops. The uprising was crushed and Philip nominated Gaius Messius Quintus Decius as governor of the province. Future events would prove this to be a mistake. Pacantius' revolt was not the only threat to his rule: in the East, Marcus Iotapianus led another uprising in response to the oppressive rule of Priscus and the excessive taxation of the Eastern provinces. Another two usurpers Marcus Silbannacus and Sponsianus are reported to have started rebellions without much success.
In April 248, Philip had the honour to lead the celebrations of the one thousandth birthday of Rome, founded in 753 BC by Romulus (see founding of Rome). According to contemporaray accounts, the festivities were magnificent and included spectacular games and theatrical presentations throughout the city. The events were also celebrated in literature, with several publications, including Quadratus's History of a Thousand Years, specially prepared for the anniversary.
Despite the festive atmosphere, discontent in the legions was growing. Decius was proclaimed emperor by the Danubian armies in the spring of 249 and immediately marched to Rome. Philip's army met the usurper near modern Verona that summer. Decius won the battle and Philip was killed, either in the fighting or assassinated by his own soldiers who were eager to please the new ruler. When the news of Decius' success reached Rome, Marcus Julius Severus Philippus, Philip's eleven-year-old son and heir, was also murdered.
Later tradition, including the historian Eusebius in his Ecclesiastical History, stated that Philip was the first Christian Roman emperor. This is doubtful because non-Christian writers do not mention the fact, and throughout his reign Philip continued to follow the state religion. Eusebius' claim is probably due to the tolerance Philip showed towards Christians.
Gordian III (238-244)