The O'Malleys had the run of the seas on the west coast and their castles were built defensively facing the sea to protect themselves and maintain control of the barony of Murrisk.
When Grace’s father, Eoin O’ Malley died, she automatically inherited his shipping and trading business. Amalgamating land her mother gave her with property from her first husband, Donal O’Flaherty, her wealth expanded rapidly and she is believed to have had more than 1,000 cattle and horses. In addition to all this, the O’Malley’s took a pirate-like attitude and charged ships an extra tax to sail in their territory. Galway was already charging taxes on ships trading in Galway Bay. Often the O’Malleys demanded some cargo before allowing the passing ships to sail into Galway.
Grainne married twice: her first marriage in 1546 to Donal O’Flaherty was considered a good match politically, as he harboured plans to rule western Connaught. They had three children and resided at Bunowen Castle, situated on the most western point in Galway and Connaught which doubled as a base for shipping and trading.
By 1566, O'Malley married Richard Burke, better known as ‘Iron Richard’. Grace’s wealth expanded even more with this union, as Burke owned Rockfleet Castle, (also called Carraigahowley Castle), near Newport, as well as other properties.
It is believed that the couple married under Brehon law 'for one year certain' and that when the year was up Grainne divorced Burke and kept the castle. Locking herself and her followers inside she shouted out a window to Burke, "Richard Burke, I dismiss you”. The pair had one son, Theobald, nicknamed "Tibbot of the Ships", who was born about 1567. Tibbot was later knighted and given the title of first Viscount Mayo in 1626 by Charles I.
In 1593, Grace’s sons, Tibbot Burke and Murrough O'Flaherty, and her half-brother, Donal of the Pipes, were held captive under the order of the British Governor, Sir Richard Bingham, Grace sailed to England to request their release from Queen Elizabeth l. O'Malley refused to recognise Elizabeth as Queen of Ireland. Some say she held a dagger in her clothing during that meeting which the guards found after searching her. Elizabeth accepted Grace’s story that she carried it for her own safety. It is also alleged that the brazen Grace threw a lace-edged handkerchief, which was given to her by the Queen when she sneezed, into a nearby fireplace, much to the dismay of the court. Elizabeth agreed to the removal of Lord Bingham from his post in Ireland and Grace promised to stop promoting the Irish Lords' rebellions. Upon her return to Ireland, her cattle, which Bingham had stolen, were not returned as promised.
Grace O'Malley concluded that her meeting with Elizabeth had been fruitless and so led Irish rebel armies during the Nine Years War. Granuaile died, aged over ninety, at Rockfleet Castle around 1603 and her tomb is believed to be in the 14th century abbey on Clare Island. The Browne family, owners of Westport House trace their ancestry back to Grace O’Malley and have a large bronze statue of her on their grounds.