Holt was a fashion designer who began with a dress shop in Melbourne in partnership with Betty James in 1930. Her biographer, P. A. Pemberton, states that she also designed packaging for her father's food processing business. In 1946, she opened another frock shop in Melbourne, Magg, which expanded to Sydney was known for its formal wear. She also played a design role in Expo '67, Montreal and redecorated The Lodge, Canberra.