Having been passed over by his father in favour of Polyperchon as his successor in the regency of Macedonia, Cassander allied himself with Ptolemy Soter and Antigonus, and declared war against the regent. Most of the Greek states went over to him, and Athens also surrendered. He further effected an alliance with Eurydice, the ambitious wife of King Philip Arrhidaeus of Macedon.
Both she and her husband, however, together with Cassander's brother, Nicanor, were soon after slain by Olympias. Cassander at once marched against Olympias, and, having forced her to surrender in Pydna, put her to death (316 BC). In 310 BC/309 BC he also murdered Roxana and nominal King Alexander IV of Macedon, the wife and son of Alexander the Great, whose natural son Heracles he bribed Polyperchon to poison.
He had already connected himself with the royal family by marriage with Thessalonica, Alexander the Great's half-sister, and, having formed an alliance with Seleucus, Ptolemy and Lysimachus, against Antigonus, he became, on the defeat and death of Antigonus around 301 BC, undisputed sovereign of Macedonia. He died of dropsy in 297 BC.
Cassander was a man of literary taste, but violent and ambitious. He restored Thebes after its destruction by Alexander the Great, transformed Therma into Thessalonica, and built the new city of Cassandreia upon the ruins of Potidaea.