He was the son of Tellis and Argileonis, and won his first laurels by the relief of Methone, which was besieged by the Athenians (431 BC). During the following year he seems to have been eponymous ephor (Xen. Hell. ii. 3, 10), and in 429 he was sent out as one of the three commissioners to advise the admiral Cnemus. As trierarch he distinguished himself in the assault on the Athenian position at the Battle of Pylos, during which he was severely wounded (Thuc. iv. II. 12).
In the next year, while Brasidas mustered a force at Corinth for a campaign in Thrace, he frustrated an Athenian attack on Megara (Thuc. iv. 70-73), and immediately afterwards marched through Thessaly at the head of 700 helots and 1000 Peloponnesian mercenaries to join the Macedonian king Perdiccas. Refusing to be made a tool for the furtherance of Perdiccas's ambitions, Brasidas set about the accomplishment of his main object, and, partly by the rapidity and boldness of his movements, partly by his personal charm and the moderation of his demands, succeeded during the course of the winter in winning over the important cities of Acanthus, Stagirus, Amphipolis and Torone as well as a number of minor towns. An attack on Eion was foiled by the arrival of Thucydides, the historian, at the head of an Athenian squadron. In the spring of 423 a truce was concluded between Athens and Sparta, but its operation was at once imperilled by Brasidas's refusal to give up Scione, which, the Athenian partisans declared, revolted two days after the truce began, and by his occupation of Mende shortly afterwards.
An Athenian fleet under Nicias and Nicostratus recovered Mende and blockaded Scione, which fell two years later (421 BC). Meanwhile Brasidas joined Perdiccas in a campaign against Arrhabaeus, king of the Lyncesti, who was severely defeated. On the approach of a body of Illyrians, who, though summoned by Perdiccas, unexpectedly declared for Arrhabaeus, the Macedonians fled, and Brasidas's force was rescued from a critical position only by his coolness and ability. This brought to a head the quarrel between Brasidas and Perdiccas, who promptly concluded a treaty with Athens, of which some fragments have survived (I.G. i. 42).
In April 422 the truce with Sparta expired, and in the same summer Cleon was despatched to Thrace, where he stormed Torone and Galepsus and prepared for an attack on Amphipolis. But a carelessly conducted reconnaissance gave Brasidas the opportunity for a vigorous and successful sally. The Athenian army was routed with a loss of 600 men and Cleon was slain. On the Spartan side only seven men are said to have fallen, but amongst them was Brasidas. He was buried at Amphipolis with impressive pomp, and for the future was regarded as the founder (olKu7ri~s) of the city and honoured with yearly games and sacrifices (see Battle of Amphipolis; Thuc. iv. 78-v. II). At Sparta a cenotaph was erected in his memory near the tombs of Pausanias and Leonidas, and yearly speeches were made and games celebrated in their honour, in which only Spartiates could compete (Paus. iii. 14). Thus the two men from both Athens and the Peloponnese who were the most open advocates of continuous war, Brasidas and Cleon, were killed in a single battle, and the way was open to a peace negotiation under more moderate leaders.
Brasidas united in himself the personal courage characteristic of Sparta with those virtues in which the typical Spartan was most signally lacking. He was quick in forming his plans and carried them out without delay or hesitation. With an oratorical power rare amongst the Lacedaemonians he combined a conciliatory manner which everywhere won friends for himself and for Sparta (Thuc. iv. 81).