It is said that Philip II had first fallen in love with Olympias when they were among the initiates into the Kabeiria Mysteries of Dionysus in the Greek island of Samothrace. Their marriage was stormy, however, and Olympias returned to Epirus in the fall of 357 BC, wintering there and having an adulterous affair. Late in spring 356 BC, under pressure from her uncle, the Epirotan king Arymbas, she returned to Pella, the Macedonian capital. Upon her return, she was pregnant, and she bore her son Alexander in late July 356 BC. Not long afterwards (late spring 355 BC) she also bore Philip a daughter, Cleopatra.
Despite the arrival of his first legitimate son (he had already fathered another illegitimate son, Philip III), Philip II was scorned for having a child not of "pure Macedonian blood". Angry at her husband for not accepting Alexander, Olympias insisted it was Zeus, King of the Gods, who had impregnated her while she slept under an oak tree (which were sacred to him). Alexander appeared to have believed the tale, as he later sought confirmation of his divine descent at the sanctuary of Zeus Ammon (of the sands) in the Siwa Oasis in Egypt.
Olympias was angered by Philip's marriage to Cleopatra Eurydice, in 337 BC. She was not angry because Philip had chosen a new woman to be his wife — indeed, he had several lovers, both male and female, and multiple wives — but because upon marrying Eurydice he divorced Olympias and disowned their son, Alexander. At the wedding banquet, Cleopatra Eurydice's guardian Attalus wished that the new couple would produce "legitimate heirs" together.
Accompanied by Alexander, Olympias withdrew for approximately a year to Epirus, where her brother Alexander I of Epirus was now king. She and her son returned to Pella after an apparent reconciliation, or at least cessation of hostilities; Philip had cemented his ties to Alexander I by offering him the hand of his and Olympias' daughter Cleopatra in marriage. At Philip's wedding soon afterwards, he was murdered; it is unclear whether Olympias had anything to do with its planning, but unlikely that Alexander, her son, was in on the murder. It is only known for sure that Alexander had the body of Philip's assassin (Pausanias of Orestis) chained to stakes and left on public display to starve as a criminal (apotumpanismos. The head of the body of Pausanias was found to have on it a golden crown, supposedly put there by Olympias. Pausanias' body was ultimately taken down from the crucifixion cross and placed over Philip's body. The two were cremated together in a typical Macedonian rite. Olympias dedicated a memorial to Pausanias. The sword used by Pausanias to kill Philip was hung in the temple of Apollo at Delphi, per special orders from Olympias herself, under the name Mistilis.
Olympias murdered Caranus, son of Philip and his last wife, Cleopatra Eurydice. She also murdered Caranus's sister, Europa, and forced Cleopatra Eurydice to hang herself. During the absence of Alexander, with whom she regularly corresponded on public as well as domestic affairs, she wielded great influence in Macedon, causing trouble to the regent, Antipater.
Upon Alexander's death in 323 BC, Olympias withdrew again into Epirus. She supported her grandson Alexander, son of Alexander the Great, and in 317 BC, allied with Polyperchon who had succeeded Antipater in 319 BC. Olympias took the field with an Epirote army in an attempt to drive Cassander, Antipater's son, from power in Macedon.
When she engaged Eurydice III (Philip's granddaughter through his wife Audata) in battle, Eurydice's troops defected to Olympias, unwilling to fight against the mother of Alexander. Olympias imprisoned Eurydice and her husband Philip Arrhidaeus; he was executed and Eurydice was forced to hang herself. For a short period Olympias was mistress of Macedonia.
Cassander hastened from Peloponnesus, and, after an obstinate siege, compelled the surrender of Pydna, where Olympias had taken refuge. One of the terms of the capitulation had been that Olympias' life should be spared. In spite of this, she was brought to trial for the numerous and cruel executions of which she had been guilty during her short span of power. Condemned without a hearing, she was put to death in 316 BC by the friends of those whom she had slain. Cassander is said to have denied her remains the rites of burial.