Plato's philosophical career developed from the intellectual circle of Socrates and the political upheavals of Athens. Socrates's trial and execution in 399 BCE became a defining subject in Plato's writing, though his dialogues are crafted philosophical works rather than transcripts. Travels after that event are reported in later sources, including visits to southern Italy and Sicily. Some details, including the precise circumstances of his encounters with rulers, remain uncertain. His political engagement extended beyond theories about the best government.

Around 387 BCE Plato established the Academy in Athens. It became a centre for sustained discussion, mathematical inquiry and philosophical education, and Aristotle studied there for twenty years. Plato's later visits to Syracuse involved attempts to influence Dionysius II, encouraged by his associate Dion. The effort failed amid court suspicion and political conflict. Surviving letters associated with these events are important evidence, but their authorship and reliability are debated.

Plato wrote dialogues exploring justice, knowledge, love, education, language, the soul and the relationship between appearance and reality. The Apology presents a defence of Socrates; the Phaedo and Symposium develop arguments through dramatic conversation; the Republic connects political organization with a broad account of ethical and intellectual education. His theory of Forms treats objects of knowledge as more stable than the changing things encountered by the senses. Particular dialogues develop different arguments, and their speakers' claims cannot always be assigned directly to Plato as a single fixed doctrine.

The Republic's philosopher-rulers and its criticism of democratic political culture have provoked lasting disagreement. Its proposals regarding education, censorship and the organization of family life are central to that debate, rather than incidental features of an otherwise timeless ideal. In the Laws, probably a late work, Plato examines a more detailed legal and institutional order. His writings preserved Socratic questioning while moving beyond it toward extensive accounts of reality and government. He died in Athens around 348–347 BCE. The Academy continued after him, and later Platonist traditions repeatedly reinterpreted his work. His career left an enduring model of philosophy as inquiry conducted through argument, dialogue and the testing of assumptions about how human beings should live.