He was a native of Cardia in the Thracian Chersonese. At a very early age he was employed as private secretary by Philip II of Macedon, and, after the death of Philip II, by Alexander the Great, whom he accompanied into Asia. After Alexander's death (323 BC), Eumenes took command of a large body of Macedonian and Greek soldiers fighting in support of Alexander's son, Alexander IV. In the ensuing division of the empire, Cappadocia and Paphlagonia were assigned to Eumenes; but as they were not yet subdued, Leonnatus and Antigonus were charged by Perdiccas with securing them for him. Antigonus, however, ignored the order, and Leonnatus vainly attempted to induce Eumenes to accompany him to Europe and share in his far-reaching designs.
Eumenes joined Perdiccas, who installed him in Cappadocia. When Craterus and Antipater, having subdued Greece in the Lamian War, determined to pass into Asia and overthrow the power of Perdiccas, their first blow was aimed at Cappadocia. Craterus and Neoptolemus, satrap of Armenia, were completely defeated by Eumenes in a battle somewhere near the Hellespont in 321 BC. Neoptolemus was killed, and Craterus died of his wounds.
After the murder of Perdiccas in Egypt by his own soldiers (320 BC), the Macedonian generals condemned Eumenes to death, assigning Antipater and Antigonus as his executioners. Eumenes, betrayed to them by one of his own officers, fled to Nora, a strong fortress on the border between Cappadocia and Lycaonia, where he held out for more than a year, until the death of Antipater threw his opponents into disarray. Antipater had left the regency to his friend Polyperchon instead of his son Cassander. Cassander therefore allied himself with Antigonus and Ptolemy, while Eumenes allied himself with Polyperchon. He was therefore able to escape Nora, and his forces were soon threatening Syria and Phoenicia.
In 318 BC Antigonus marched against him, and Eumenes withdrew east to join the satraps of the provinces beyond the Tigris River. After two indecisive battles at Paraitacene (317 BC) and Gabiene (316 BC), Eumenes was betrayed to Antigonus by his own soldiers.
According to Plutarch and Diodorus, Eumenes had won the battle but lost control of his army's baggage camp. This baggage was all the loot which the Macedonian veterans (called the Argyraspids, or Silver Shields) had accumulated over 30 years of successful warfare. It contained not only gold and gems but the Greeks' women and children. Antigonus sent a message to the Silver Shields saying he would give back all their baggage if they gave him Eumenes. The Silver Shields handed over Eumenes. Antigonus, after some consideration, had his enemy executed.
The Macedonians in his army were openly skeptical of Eumenes. Despite his undeniable skills as a general, he never commanded their full allegiance and died as a result. He was an able soldier who did his utmost to maintain the unity of Alexander's empire in Asia; but his efforts were frustrated by the generals and satraps, who hated and despised him as a non-Macedonian general and mere secretary. Eumenes is a tragic figure, a man who seemingly tried to do the right thing but was overcome by a more ruthless enemy and the treachery of his own soldiers.
- Historie, a manga based on Eumenes' life.
- Plutarch - the main surviving biography of Eumenes is by Plutarch. Plutarch's parallel Roman life was the life of Sertorius.
- Diodorus - Eumenes is a significant figure in books 16-18 of Diodorus's history