At fifteen, Emma met Sir Harry Fetherstonhaugh, who hired her for several months as hostess and entertainer at a lengthy stag party at Fetherstonhaugh's Uppark country estate in the South Downs. She is said to have entertained Harry and his friends by dancing in the nude on the dining room table. Fetherstonhaugh took Emma there as a mistress, but frequently ignored her in favour of drinking and hunting with his friends. Emma soon formed a friendship with one of the guests, the dull but sincere Honourable Charles Francis Greville (1749–1809), second son of the then Earl of Warwick and a member of Parliament for Warwick. It was about this time (late June-early July 1781) that she conceived a child. Fetherstonhaugh was rumoured to be the father.

Dame Emma Hamilton (26 April 1765; baptised 12 May 1765 – 15 January 1815), generally known as Lady Hamilton, was an English model and Actress, who is best remembered as the mistress of Lord Nelson and as the muse of the portrait Artist, George Romney.

To be rid of Emma, Greville persuaded his uncle, Sir william Hamilton, British Envoy to Naples, to take her off his hands. Greville's marriage would be useful to Sir william, as it relieved him of having Greville as a poor relation. To promote his plan, Greville suggested to Sir william that Emma would make a very pleasing mistress, assuring him that, once married to Henrietta Middleton, he would come and fetch Emma back. Emma's famous beauty was by then well-known to Sir william, so much so that he even agreed to pay the expenses for her journey to ensure her speedy arrival. A great collector of antiquities and beautiful objects, he took interest in her as another acquisition. He had long been happily married until the death of his wife in 1782, and he liked female companionship. His home in Naples was well known all over the world for hospitality and refinement. He needed a hostess for his salon, and from what he knew about Emma, he thought she would be the perfect choice.

In 1783, Greville needed to find a rich wife to replenish his finances (in the form of eighteen-year-old heiress Henrietta Middleton). Emma would be a Problem, as he disliked being known as her lover (this having become apparent to all through her fame in Romney's artworks), and his prospective wife would not accept him as a suitor if he lived openly with Emma Hart.

Living in Naples, Emma developed what she called her "Attitudes" or Mimoplastic art, using Romney's idea of combining classical poses with modern allure as the basis for her act. Emma had her dressmaker make dresses modelled on those worn by peasant islanders in the Bay of Naples, and the loose-fitting garments she often wore when modelling for Romney. She would pair these tunics with a few large shawls or veils, draping herself in folds of cloth and posing in such a way as to evoke popular images from Greco-Roman mythology. This cross between postures, dance, and acting was first revealed in spring 1787 by Sir william to a large group of European guests at his home in Naples, who quickly took to this new form of entertainment. It formed a sort of charade, with the audience guessing the names of the classical characters and scenes Emma portrayed.

Emma Hamilton is generally known by the courtesy title of "Lady Hamilton", which she was entitled to from 1791 as the wife and then widow of Sir william Hamilton, but in 1800, she became "Dame Emma Hamilton", a title she held in her own right as a female member of the Order of Malta.

As wife of the British Envoy, Emma welcomed Nelson in 1793, when he came to gather reinforcements against the French. She is described in 1797 in the diary of 18-year-old Elizabeth Wynne as "a charming woman, beautiful and exceedingly good humoured and amiable." Nelson returned to Naples five years later, on 22 September 1798 (with stepson, Josiah, who was in his early twenties), a living legend, after his victory at the Battle of the Nile in Aboukir.

In 1799, Naples was the scene of a strange revolution led by members of the aristocracy; the Common people did not agree with the revolution. The French troops were not welcome, but the royal family fled to Sicily. From here Nelson tried to help the royal family put down the Revolutionaries. He had absolutely no support from the British government. He even executed one of the Leaders of the revolution, Admiral Francesco Caracciolo. Emma Hamilton tried to draw a parallel between the revolution in Naples and the Irish uprising in 1798.

Emma gave birth to Nelson's daughter Horatia, on 29 January 1801 at Sir William's rented home in Clarges Street, 23 Piccadilly, London. By the autumn of the same year, Nelson bought Merton Place, a small ramshackle house on the outskirts of modern-day Wimbledon. There he lived openly with Emma, Sir william, and Emma's mother, in a ménage à trois that fascinated the public.

Sir william died in 1803, and Nelson returned to sea soon after to fight in the Napoleonic Wars, leaving Emma pregnant with their second child. She was desperately lonely, preoccupied with attempting to turn Merton Place into the grand home Nelson desired, and frantic for his return. The child, a girl, died a few weeks after her birth in early 1804. Emma reportedly distracted herself by gambling, and spending lavishly. Now she was free to marry Nelson, if he could only obtain a divorce.

After Nelson's death in 1805 at the Battle of Trafalgar, an annuity from Sir William's estate could have ensured a comfortable, if modest, lifestyle for Emma. However she quickly exhausted this small pension and fell deeply into debt. Nelson had willed his estate to his brother; he gave Merton Place to Emma, but she depleted her finances by trying to keep it up as a monument to him. In spite of Nelson's status as a national hero, the instructions he left to the government to provide for Emma and Horatia were ignored. They showered honours on Nelson's brother instead.

Subsequently, she used her new title in formal circumstances, and was also acknowledged as "Dame Emma Hamilton" in official British contexts; most notably, this was the title under which she was formally granted her own coat of arms by the English College of Arms in 1806, Per pale Or and Argent, three Lions rampant Gules, on a chief Sable, a Cross of eight points of the second. The lions evidently refer to her maiden surname of Lyons, while the addition of the Maltese Cross, which has puzzled heraldic scholars unaware of her connection to the Order, is recognizable as an honourable augmentation referring to her damehood.

Emma spent a year in a virtual debtors' prison, in the company of Horatia, before moving to France (despite the ongoing Napoleonic War) to try to escape her creditors. Turning to drink, living in poverty in Calais, she died in January 1815, aged 49, of amoebic dysentery—-an illness she probably contracted during her years in Naples. Sir william Hamilton had also suffered from amoebic dysentery. Emma was buried in Calais but her grave was subsequently lost due to wartime destruction.

Horatia subsequently married the Rev. Philip Ward and lived until 1881. She had ten children: Horatio Nelson (born 8 December 1822); Eleanor Phillipa (born April 1824); Marmaduke Philip Smyth (born 27 May 1825); John James Stephen (13 February 1827–1829); Nelson (born 8 May 1828); william George (born 8 April 1830); Edmund Nelson (1831); Horatia Nelson (born 24 November 1833), Philip (born May 1834) and Caroline (born January 1836).

Emma nursed Nelson under her husband's roof, and arranged a party with 1,800 guests to celebrate his 40th birthday. They soon fell in love and their affair seems to have been tolerated, and perhaps even encouraged, by the elderly Sir william, whose own health was now failing and who longed for retirement.

Nelson's recall to Britain shortly afterwards coincided with the government finally granting Hamilton's request for relief from his post. Nelson, Emma and william therefore travelled together—-taking the longest possible route back to Britain via Central Europe (hearing the Missa in Angustiis by Joseph Haydn, now known as the "Nelson Mass" in Vienna in 1800), and eventually arriving in Britain to a hero's welcome. The three then lived together openly, and the affair became public knowledge and scandal, which eventually induced the Admiralty to send Nelson back to sea, if only to get him away from Emma.