It is shown from our sources that in the first year of the war, Brasidas was in the southwest of the Peloponnese serving near Messene. When the Athenian fleet attacked the port of Methone, he rushed to the town to support its defenders, and was able to save it.Through this he had a siginificant impact on the war in that he gave the spartans a psychological advantage as it was one of the few Spartan successes in the first year of the war. Thucydides adds that "because of this, Brasidas was the first man in this war to receive official honors at Sparta". This action of bravery by Brasidas amongst others could explain why Thucydides is perhaps sometimes biased towards him.
In 425, the war entered its seventh year. The Athenians had already discovered that the strategy of Pericles was too expensive. Sparta was slower to develop a new strategy, and it was Athens that first embarked upon a new course. In the spring of 425 the Athenian expedition to Sicily led by Sophocles and Eurymedon, which was on its way to Corcyra at this time, was asked for support in building a strategic fort near Pylos by the Athenian General Demosthenes. By this the Athenians wanted to build a strategic stronghold close to Sparta itself while being able to easily control the western sea of the peloponnese. It could be useful as a base for further raids in the region, and offered helots an opportunity to escape, which would cripple the Spartan economy. The request was denied however and Demosthenes‘ men needed to built the fortifications for themselves.
Sparta immediately sent troops, which included Brasidas, who commanded a trireme. Using the isle of Sphacteria as their base, the Spartans tried to land near Pylos, and Brasidas was among the most daring captains: instead of ordering his soldiers to jump into the sea and walk to the land, he simply ran his ship ashore for the others to follow his example which is another example of his bravery. The amphibious assault did however not succeed as Brasidas was severely wounded and the Athenians were superior recovering his shield and using it as a trophy, the Spartan navy was defeated, and no less than 292 Spartan soldiers, including 120 elite Spartiates, were cut off on Sphacteria and approximately a further 148 were killed in action. In a second operation, they were captured by the Athenian commander Cleon. This action according to Thudcydides „caused much more surprise among the Hellenes than anything else that had happened in the war. The general impression had been that the Spartans would never surrender their arms whether because of hunger or any other form of compulsion ;instead they would keep them to the last and die fighting as best they could.“ This clearly shows that the campaign at Pylos and Brasidas‘ intervention had a strong impact upon the war in that it changed the general mindset of most Hellenes whilst partly damaging Brasidas‘ reputation.
The Spartan defeat made it clear that Sparta had to rethink its options. Athens refused to negotiate and pillaging Attica was no longer possible as the captives would be executed and that was unbearable as they were of Dorian blood. An opportunity, however, offered itself, when the Macedonian king Perdiccas II requested Spartan help. Brasidas himself suggested to accept the invitation and send an army to the north, where it could attack the Athenian allies on the Khalkidike.
As Sparta could hardly afford to send away many Spartiates, who were now needed on the Peloponnese to control the helots of Messenia. In the end, Brasidas received an army of 700 loyal, liberated, and armed helots. Brasidas proceeded to Sicyon and Corinth, where he wanted to recruit additional forces.
He was finally reinforced with 1000 men after intervening at Megara and then continued to Thebes, Thessaly, and Macedonia, where king Perdiccas demanded the help he had requested .He immediately opened negotiations with the Lyncestian