Gillie Hoyte Byrom began enamelling in 1977 and was largely self-taught until 1990 when she went to Barcelona to learn the painting of portrait miniatures in vitreous enamel. These specialist techniques, as practised in the eighteenth century, involve firing each miniature in a kiln at about 750ºC at least a dozen times, gradually modelling the portrait in vitreous enamel paint, using the finest miniaturist's brushes and fusing the glass metal oxide pigments at each firing. The resultant piece is durable and its colours never fade.

Gillie paints portrait miniatures to commission and in recent years has become established as an enamel portrait miniaturist in the London market. She exhibits annually with the Royal Society of Miniature Painters, Sculptors and Gravers in London and regularly with the Hilliard Society of Miniaturists in Wells, the British Society of Enamellers, and the Devon Guild of Craftsmen. She is Chair elect of the Guild of Enamellers. Gillie submits her work annually to the Goldsmiths' Craft Council Competition and has won the top award in enamel painting every year since 1995.

Gillie enjoys writing articles on enamelling and portrait miniatures. She has built up a collection of images of her work, not only to show finished pieces but also the vitreous enamelling process and she offers lectures on this theme. At Somerset House, she has run workshops together with an art historian, on the enamel portrait miniatures in the Gilbert Collection. She has travelled widely with her husband Peter on textile business and has always taken a keen interest in researching contemporary enamelling in the countries they have visited, such as India, Turkey and China. She was invited to teach enamel painting in Beijing in 2005.