He is a contemporary American author of children books, photo-illustrator and watercolor artist living in Shapleigh, Maine. Born in Massachusetts, he grew up in Bangor, and Kennebunk, Maine. He received a degree in biology from the University of Maine. In addition to his 45 children's books, seven of them set in Iceland, he has authored two books of humor, Punography, featured in Life magazine, and Punography Too..

McMillan's watercolor art has been in numerous juried shows in New England and Iceland. His 2018 Winter Olympics curling watercolors were a two-page feature in the Maine Sunday Telegram Arts Section. His watercolor Browns Head Light Vinalhaven was Best in Show at the Port Clyde (Maine) Art Gallery Third Annual Invitational 10 x 10 Show in 2017. His watercolors are in private collections in the US, Canada, Iceland, and Switzerland.