Hugh Douglas Hamilton was an Irish portrait-painter. He spent considerable periods in London and Rome before returning to Dublin in the early 1790s. Until the mid-1770s he worked mostly in pastel. His style influenced the English painter Lewis Vaslet (1742–1808).

Hamilton was born in Crow Street, in Dublin, Ireland, in 1740, the son of a peruke maker. Unfortunately there is very little concrete evidence for his early life, apart from his own drawings. He studied art under Robert West and James Mannin at the Dublin Society House - and won some early success with crayon and pastel portraits there. He was very adept at building relationships with patrons from the early days, taking up with the famous La Touche banking family of Dublin, who had close ties with the Bank of Ireland.

Very little is known of Hamilton's career between 1756 and 1764, when he moved to London. Hamilton found great success in London through his pastel oval portraits, portraying royalty, politicians and celebrities of the day through this medium. Hamilton was often overwhelmed with orders, including commissions from the British royal family - such as Queen Charlotte (1764) and others now in the British Royal Collection. He showed with the Society of Artists and the Free Society of Artists from the mid-1760s to the mid-1770s. From the mid-1770s on, Hamilton became very interested in a softer, more textural form of pastel "fresco", in which he blended crayons and chalk to further the pastel's ability to imitate flesh.

In 1779 he travelled to Italy, where he remained for the next twelve years, occasionally visiting Florence but mainly based in Rome, where he knew Antonio Canova. On the advice of artist John Flaxman Hamilton turned to oil painting, and achieved great success with small oval portraits of Irish and British visitors. His portraits of this period include those of Dean Kirwan (displayed at the Royal Dublin Society), George John, 2nd Earl Spencer, Countess Cowper (1787), and the exiled Charles Edward Stuart ( Lord Edward, 1785).

In 1791 Hamilton returned to Dublin, where he died. In 1796 he painted Lord Edward Fitzgerald, the Irish revolutionary.