Kate McMullan was born in St. Louis, Missouri. As a small child, she listened as her father read the comics aloud and her mother shared books and poems. When she got old enough, she began reading her way through the public library.

She taught fourth and sixth grades in inner-city Los Angeles and on an American Air Force base in Germany before becoming an editor of language arts and audiovisual materials for a publishing house. Her first children's book was published in 1976, and since that time she has written early 100 books for children. Some of her books are written under her maiden name Katy Hall, while others are written under her married name, Kate McMullan or K.H. McMullan. Her husband, Jim McMullan has illustrated many of her books.