Ptolemy was probably still alive c. 180. No other certain details are known about his life; Harnack's suggestion that he was identical with the Ptolemy spoken of by St. Justin is as yet unproved. It is not known when Ptolemy became a disciple of Valentinius, but Valentius was active in the Egyptian city of Alexandria, and in Rome. Ptolemy was, with Heracleon, the principal writer of the Italian or Western school of Valentinian Gnosticism, which was active in Rome, Italy, and Southern Gaul.
Ptolemy's works have reached us in an incomplete form as follows:
The latter is found in the works of Epiphanius. It was written in response to Flora's inquiry concerning the origin of the Law of the Old Testament. The Decalogue , Ptolemy states, cannot be attributed to the Supreme God, nor to the devil; indeed, the set of laws does not even proceed from a single law-giver. A part of it is the work of an inferior god, analogous to the gnostic demiurge; the second part is attributable to Moses, and the third part to the elders of the Jewish people. As well as this, Ptolemy subdivides the part of the Decalogue ascribed to the inferior god into three further sections:
It includes such precepts as circumcision, fasting, and was raised by the saviour from a sensible to a spiritual plane. The god who is the author of the law, insofar as it is not the product of human effort, is the demiurge who occupies a middle position between the Supreme God and the devil. He is the creator of the material universe, is neither perfect, nor the author of evil, but ought to be called 'just', and benevolent to the extent of his abilities.
In his cosmogonic depiction of the universe, Ptolemy referred to an extensive system of aeons, emanated from a monadic spiritual source. Thirty of these, as he believes, rule the higher world, the pleroma. This system becomes the basis of an exegesis which discovers in the prologue of St. John's Gospel the first Ogdoad.