Nicias, a moderate, opposed the policies of the radical democrats. During the period following the death of Pericles in 429 B.C., he emerged as Cleon’s principal opponent. He was rich and willingly undertook liturgies and the organisation of festivals.

His main achievement of the Peloponnesian War was the conclusion of a peace with Sparta which secured favourable terms for Athens. Because of his pivotal role in bringing an end to first phase of the Peloponnesian War in 421 B.C., the peace became known as the Peace of Nicias. He was opposed to the ambitious plans of Alcibiades to send an expeditionary corps to Sicily, but despite his objections, he was elected alongside Alcibiades and Lamachus general of the expedition. His moderate and indecisive military tactics contributed to a great extent to the unsuccessful outcome of the expedition following the recall of Alcibiades to Athens, the death of Lamachus and the arrival of the Spartan Gylippus (415-3 B.C.). Thucydides, despite partially defending Nicias’ policies and underlining his dedication to the city, imputed the Athenian disaster to a great extent onto the inadequacy of his military leadership.