Mark graduated from the Central Technical School Art Program in 1966, and has been a working artist since that time. He has worked as an illustrator, a designer and has shown as a gallery artist. He has taught life drawing anatomy and illustration/design at the Toronto School of Art, anatomy/figure drawing at OCAD, and picture-book illustration and figure drawing at Central Technical School. Currently, he teaches anatomy/figure drawing in the Classical Animation department at Sheridan College.
He is best known as a children's author illustrator. He has written and illustrated 16 books and designed and illustrated more than 25 books for other authors. He was co- creator and illustrator of the "Mighty Mites", a scientific comic, in Owl Magazine. From 1976 to 1991, he co-authored (with Emily Hearn) and illustrated 153 episodes. He has appeared on TVO Kids, Romper Room, Mr. Dress-up, Polka Dot Door and Caribou Club.
As an author/illustrator he has toured Canada extensively, sharing his stories and ideas with children and teachers in hundreds of schools. "Constant touring means being on the road, I'm a travelling salesman -- only I'm selling information, ideas and inspiration."