About his earlier life nothing is known. He may have been a mercenary in the service of Alexander, or simply an adventurous Athenian, but either way by 323 BC he was “the man who made it his business to take charge of unemployed soldiers when they reached the coast. To find ships for their passage to Greece, and to concentrate them at Taenarum when they arrived.”
According to Plutarch, he was responsible for the return to Greece of at least 50,000 men, against Alexander’s decrees. He may have led a contingent home himself. When Alexander died in 323 BC, Leosthenes was apparently the effective commander of the largest mercenary force in the Greek world. He seems to have taken money from Hyperides and the extreme anti-Macedonian faction in Athens to maintain this army, and then took the field along with 7000 Athenian hoplites and other allied troops against Antipater in the Second Lamian War. Phocion, the greatest Athenian soldier of the age (already quite old by this time) complimented the mercenaries, saying that they would “do well for the sprint” (were good athletes). Leosthenes defeated Antipater at least once and perhaps twice and shut him up in Lamia for a long siege. Leosthenes himself was killed in the siege, but his army went on to win another victory against a Macedonian relief force before the usual centripetal force of Greek city-state politics handed victory to Antipater. Leosthenes, with Phocion, was one of the historical characters that helped shape my ideas about Kineas.