He was a member of a distinguished family, and possessed great wealth which he expended on his friends, while content to lead the life of an athlete. In 384 he served in a Theban contingent sent to the support of the Spartans at Mantineia, where he was saved, when dangerously wounded, by Epaminondas.
Upon the seizure of the Theban citadel by the Spartans (382 BC) he fled to Athens, and took the lead in a conspiracy to liberate Thebes. In 379 his party surprised and killed their chief political opponents, and roused the people against the Spartan garrison, which surrendered to an army gathered by Pelopidas.
In this and subsequent years he was elected boeotarch, and about 375 he routed a much larger Spartan force at Tegyra (near Orchomenus). This victory he owed mainly to the valour of the Sacred Band, an elite corps of 150 pairs of male lovers. At the battle of Leuctra (371) he contributed greatly to the success of Epaminondas's new tactics by the rapidity with which he made the Sacred Band close with the Spartans.
In 370 BC he accompanied his friend Epaminondas as boeotarch into Peloponnesus. On their return both generals were unsuccessfully accused of having retained their command beyond the legal term.
In 369, in response to a petition of the Thessalians, Pelopidas was sent with an army against Alexander of Pherae. After driving Alexander out, he passed into Macedon and arbitrated between two claimants to the throne. In order to secure the influence of Thebes, he brought home hostages, including the king's brother, afterwards Philip II, the conqueror of Greece.
Next year Pelopidas was again called upon to interfere in Macedonia, but, being deserted by his mercenaries, was compelled to make an agreement with Ptolemaeus of Alorus. On his return through Thessaly he was seized by Alexander of Pherae, and two expeditions from Thebes were needed to secure his release.
In 367 Pelopidas went on an embassy to the Persian king and induced him to prescribe a settlement of Greece according to the wishes of the Thebans. In 364 BC he received another appeal from the Thessalian towns against Alexander of Pherae. Though an eclipse of the sun prevented his bringing with him more than a handful of troops, he overthrew the tyrant's far superior force on the ridge of Cynoscephalae. However, wishing to slay Alexander with his own hand, he rushed forward too eagerly and was cut down by the tyrant’s guards. See Battle of Cynoscephalae.