Marianne was born in Windsor, in New South Wales. She is the youngest child of Joseph Michael and Mary Violet Mizzi. She spent her early childhood living in a house along the Hawkesbury River. When a flood destroyed the property, the family moved to a small farm on the edges of Sydney. Marianne developed a love for reading at an early age, and became a school librarian at the age of nine. She went to high school in western Sydney. The first novel that had an influence on her was "Oliver Twist".