Regent of Scotland and soldier. Hamilton was the son of James, the 1st Earl of Arran (1475 - 1529) and, through his mother, great-grandson of King James II (1430-60). This gave rise to Hamilton's claim to the throne of Scotland. His half-brother Sir James Hamilton of Finnart (d.1540) acted as his guardian, following the death of their father.
Hamilton became Regent on the death of King James V (1512 - 1542) and gained his French Duchy for negotiating the marriage of the young Mary, Queen of Scots (1542 - 1587) to the Dauphin of France (1549). He demitted the Regency in favour of Mary of Lorraine (1515-60) in 1554 on condition that he would get the Crown if the young Mary died childless, however his claim seemed lost when it became clear that the succession was promised to France. However this planned succession did not take place when Mary's husband, by then King Francis II of France, died. Hamilton then tried unsuccessfully to arrange a marriage between Mary and his son, another James (c.1537 - 1609).
Hamilton's sympathies swayed between support for Queen Mary and the Protestant nobles who wished to see her removed, undoubtedly because he still hoped to fall heir to the throne. He withdrew to his French estates in 1565, returned in 1569, was arrested by Regent Moray (1531-70) and finally signed the Pacification of Perth (1572) in which he acknowledged the succession of King James VI (1566 - 1625).