Gillian McMillan has been a Guggenheim conservator since 1984. She has conducted numerous technical and scientific examinations and has led the conservation treatment of paintings from the early modern period in the Solomon R. Guggenheim Founding Collection and the Thannhauser Collection. Signature works treated by McMillan include paintings by Paul Cézanne, Vincent van Gogh, Édouard Manet, Fernand Léger, Jackson Pollock, and Vasily Kandinsky. McMillan is particularly engaged in a long-term research project investigating the Guggenheim's renowned paintings by Kandinsky.
McMillan holds a Diploma in the Conservation of Easel Paintings from Gateshead Technical College, United Kingdom, and served her internship at the Intermuseum Conservation Association, Oberlin College, Ohio. Prior to her Guggenheim appointment, McMillan was a paintings conservator at the Art Gallery of New South Wales in Sydney, Australia.