Megillus of Sparta is known exclusively as a character in Plato's dialogue Laws, where he is identified as a Spartan. He participates in the discussion on founding a colony and formulating its legal code alongside the Athenian Stranger and the Cretan Clinias. The dialogue portrays him as an elderly Spartan gentleman who represents the Dorian perspective on law and society. No independent biographical information exists.

No independent works by Megillus are attested. He appears solely as a character in Plato's Laws.

His significance is literary and philosophical, derived from his role in Laws. As an interlocutor, he embodies the Spartan constitutional tradition, which Plato critically examines and synthesizes with philosophical principles. His character facilitates a comparative analysis of Greek political systems and models the law-abiding civic virtue the dialogue's proposed laws intend to cultivate.