Hamilton, Gustavus (c.1739–1775), miniaturist, was one of the younger children of the Rev. Gustavus Hamilton, vicar of Errigal in the diocese of Clogher, rector of Gallen, Co. Meath, and formerly curate in Enniskillen in 1721–2, when he married his wife Jane (née Cathcart). The family claimed descent from the Hamiltons of Priestfield, Midlothian, Scotland. Hamilton was taught by Robert West (qv) at his academy in George's Lane, Dublin, which from the 1740s benefited from the patronage of the Dublin Society. The minutes of the Society's meetings record the premiums Hamilton was awarded for drawing (1755, 1756). On leaving the academy Hamilton was apprenticed to Samuel Dixon (qv) of Capel St. There he was employed, along with the miniaturists James Reily (qv) and Daniel O'Keefe (1740–87), in colouring the basso-relievo prints of birds and flowers produced by Dixon.
Hamilton and James Reily were painting miniature portraits throughout the 1750s and 1760s. They form the second generation of miniaturists who painted in watercolour on ivory, on a relatively small scale, working in the ‘modest’ manner established by Nathaniel Hone (qv) in the 1740s and 1750s. This group also included O'Keefe and Thomas Boulger (fl. 1761–88). Miniatures by Luke Sullivan (qv), Hamilton, and Reily are a crucial stylistic and technical link between the early Irish-born miniaturists such as Hone and Rupert Barber (qv) and those who excelled in the last quarter of the eighteenth century. The 1750s were a critical and formative decade in the history of watercolour-on-ivory miniature-painting in Ireland. It was in this decade that a tradition of miniature painting was established in Dublin, and it marked the establishment of the watercolour-on-ivory technique that would henceforth dominate miniature portraiture in Ireland. Miniaturists born or trained in Ireland made a significant contribution to the establishment of watercolour-on-ivory miniature portrait as the main technique for the rest of the eighteenth century. Hamilton and Reily were part of the group and were also responsible for helping to establish Dublin as the important centre of miniature patronage that it would become in the latter part of the eighteenth century.
Hamilton's miniatures are small in size and were intended to be worn in lockets and bracelets. His miniature portraits vary in quality, and the pose of his sitters is often rather stiff. A feature common to most of his work is the way the pupils of the eye and eyelashes are painted in very dark brown and black, and tend to be exaggerated in size. Like Reily, he often shaded the face with a stippled blue tinge. A good example of Hamilton's miniature style is his portrait of the Rev. Joshua Nunn (NGI). The uneven shading around the sitter's head is reminiscent of the work of the English miniaturist Samuel Collins (1735–68). Collins was in Dublin from 1762 until his death, where he had a good practice and where Hamilton may have known his work. Hamilton continued to refine the watercolour-on-ivory technique by using minute stipple brushstrokes that varied slightly in tone. In his ‘Portrait of an unknown gentleman’ (NGI) he skilfully used a contrasting light and dark background to highlight the sitter's face and add depth to the portrait. Although some of his portraits have a rather flat appearance as a result of using too much gouache, this has been avoided in this portrait by painting in pure watercolour.
He exhibited miniatures at the Society of Artists in Ireland in Dublin (1765–73), but unfortunately none of the miniatures are identifiable from the catalogue. During this period Hamilton lived at Parliament St.; 1 Dame St., College Green; and (shortly before his death) at Cork Hill. He died 16 December 1775, aged 36, and was buried on 18 December at St Werburgh's, Dublin, where a plaque was erected in his memory.