Within three months of sitting for it she left England for Naples in the protection of Greville's widower uncle, the British Ambassador Sir William Hamilton. Emma found that Hamilton's kindness in Naples suited her warm and extravagant personality. She acquired fluent Italian (with a Lancashire accent) and became famous for her 'attitudes' – solo mime performances based on classical mythology. She achieved formal respectability by her marriage to Hamilton in 1791, who described her as more beautiful than 'anything found in nature; and finer in her particular way than anything that is to be found in antique art'.

Through Hamilton, Emma first met Horatio Nelson in 1793, a friendship which turned into a mutual passion after he returned wounded to the Hamiltons' care at Naples, after the Battle of the Nile in 1798. From then until Hamilton's death in 1803 their almost inseparable 'ménage à trois' was sustained by Hamilton's refusal to acknowledge the real nature of his wife's relationship with their 'dear friend' Nelson and the lovers' genuine affection for him. Emma's grief at Nelson's death at Trafalgar in 1805 was inconsolable.