Demetrius was born in Phalerum, c. 350 BC. He was the son of Phanostratus, a man without rank or property, and was brother to the anti-Macedonian orator Himeraeus. He was educated, together with the poet Menander, in the school of Theophrastus. He began his public career about 325 BC, at the time of the disputes concerning Harpalus, and soon acquired a great reputation by the talent he displayed in public speaking. He belonged to the pro-oligarchic party of Phocion; and he acted in the spirit of that statesman. When Xenocrates was unable to pay the new tax on metics (foreign residents) c. 322 BC, and the Athenians threatened him with slavery, he was only saved (according to one story) when Demetrius purchased his debt and paid his tax. After the death of Phocion in 317 BC, Cassander placed Demetrius at the head of the administration of Athens. He filled this office for ten years, instituting extensive legal reforms. The Athenians conferred upon him the most extraordinary distinctions (almost all of which were revoked after his later expulsion from Athens), and no fewer than 360 statues were erected to him. However, Demetrius was unpopular with the lower classes of Athenians and with pro-democratic political factions, who resented the limitations he placed on the democratic franchise and viewed him as little more than a pro-Macedonian puppet ruler.