Leosthenes (in Greek Λεωσθένης; died 323 BC) was an Athenian who was commander of the combined Greek army in the Lamian War. Leosthenes is usually identified as the son of that Leosthenes who had suffered exile in 362/1 BC (Diodorus Siculus 15.95; Polyaenus 6.2.1–2) and who had fled to the court of Philip II.It is unknown by what means he had obtained the high reputation he had when he first makes his appearance in history. It has been generally inferred, from a passage in Strabo, that he had first served under Alexander the Great in Asia; but it now seems certain that this is a mistake, and rather the reference should have been to Leonnatus.
It is certain that when Leosthenes is first the subject of distinct mention, he is an officer of acknowledged ability and established reputation in war, but a vehement opponent of the Macedonian interest. Shortly before the death of Alexander he had collected together and brought over to Cape Taenarum a large body of the Greek mercenaries that had been disbanded by the different satraps in Asia, according to Alexander's orders.
As soon as the news of Alexander's death reached Athens, Leosthenes was despatched to Taenarus to engage the services of these 8,000 troops. From there he hastened to Aetolia, and persuaded the people of that region to join in the war against Macedonia. Their example was followed by the Locrians, Phocians, Dorians, and many of the Thessalians, as well as by several of the states of the Peloponnese. and Leosthenes, who was by common consent appointed commander-in-chief, assembled these combined forces in the neighbourhood of Thermopylae. The Boeotians, who, through fear of the restoration of Thebes, remained allied to the Macedonians, collected a force to prevent the Athenian contingent from joining the allied army. However, Leosthenes hastened with a part of his forces to assist the Athenians and totally defeated the Boeotian army.