Harris was born in Cardiff, but from the age of five she went to live with her grandparents and grew up in an isolated cottage in the Dorset countryside. As a result of being very lonely only child she had plenty of time to read and also to dream up stories which she told to her imaginary friends.

After leaving Gillingham Grammar School, she went back to Cardiff and worked as a clerk in the City Hall. It was here that she met and married a Grenadier Guardsman. She moved from Cardiff to his home on Merseyside and grew to know the Wallasey and Liverpool area.

Her writing career started as a freelance writer, writing for the Liverpool Echo and national magazines on fashion, homemaking and health topics under the by-line Marion Harris. Her first novel was published in 1975, followed by eight others all under the name Marion Harris. Additionally, she has written about twenty non-fiction books all under different pseudonyms.

Ten years later, and with three children, Harris and her family moved to Buckinghamshire where she has lived ever since. Her children have all made their homes in the area and she now has six grandchildren and one great-grandchild.

Since 2000 Harris has been writing as Rosie Harris. She has focused on romance sagas. These works are all set in the 1920s and 1930s and concentrate on strong and courageous female characters.

She is currently published by Heinemann and Arrow Books Ltd, an imprint of Random House.