His reign was inaugurated by the murder of his mother, and he was always under the dominion of favourites, male and female, who indulged his vices and conducted the government as they pleased. Self-interest led his ministers to make serious preparations to meet the attacks of Antiochus III the Great on Coele-Syria including Judea, and the great Egyptian victory of Raphia (217), where Ptolemy himself was present, secured the northern borders of the kingdom for the remainder of his reign.

The arming of Egyptians in this campaign had a disturbing effect upon the native population of Egypt, leading to the secession of Upper Egypt under pharaohs Harmachis (also known as Hugronaphor) and Ankmachis, (also known as Chaonnophris) thus creating a kingdom that occupied much of the country and lasted nearly twenty years.

Philopator was devoted to orgiastic forms of religion and literary dilettantism. He built a temple to Homer and composed a tragedy, to which his favourite Agathocles added a commentary. He married (about 220 BC) his sister Arsinoë III, but continued to be ruled by his mistress Agathoclea, sister of Agathocles.

Ptolemy is said to have built a giant ship known as the tessarakonteres ("forty"), a huge type of galley. The forty of its name may refer to its number of banks of oars. The only recorded instance of this type of vessel, in fact, is this showpiece galley built for Ptolemy IV, described by Callixenus of Rhodes, writing in the 3rd century BCE, and by Athenaeus in the 2nd century AD. Plutarch also mentions that Ptolemy Philopater owned this immense vessel in his Life of Demetrios. The current theory is that Ptolemy's ship was an oversize catamaran galley, measuring 128 m 420 ft.

Ptolemy IV is a major protagonist of the apocryphal 3 Maccabees, which describes purported events following the Battle of Raphia, in both Jerusalem and Alexandria.

This article incorporates text from the Encyclopædia Britannica Eleventh Edition

Preceded by Ptolemy III Euergetes

Succeeded by Ptolemy V Epiphanes