Lysias was the son of a well-to-do Hellene from Syracuse called Cephalus, who had migrated to Attica at the invitation of Pericles in 450 or thereabouts. It cannot have been long after this that Lysias was born. Though a metic family, Lysias and his household achieved substantial status in Athenian society. That Plato chose their house as the setting for his dialogue Republic, and that Cephalus and his sons were characters in it, was no accident.

After the capture (404) of Athens by the Spartans, the Thirty Tyrants caused the arrest of Lysias and his brother Polemarchus, who was put to death. Lysias escaped to Megara, from which he returned when the tyrants were expelled (403). Lysias' putting on trial one of the Thirty Tyrants called Eratosthenes proved to be a turning point in his life.

His prosecution speech (Versus Eratosthenes) won him a reputation as a speech-writer, and its text is regarded as one of the best specimens of the art of rhetoric. Thirty-five of his speeches have come down to us whole or in part, and of these thirty are forensic speeches written (with the exception of the 'Versus Eratosthenes') to defend a client. In those speeches which deal with relations between private persons, details of Athenian social life are frequent. This makes Lysias' works one of our best sources for private life in classical Athens.