K athryn Lasky was born on June 24, 1944 in Indianapolis, Indiana, the second daughter of Marven Lasky, a bottler, and his wife Hortense, a social worker. In Indianapolis, she attended a girl's school that encouraged writing but not necessarily imagination. Her earliest attempts at fiction she kept strictly to herself; it was not until reaching adulthood that Lasky accepted writing as a legitimate occupation for herself. She left home to attend college at the University of Michigan, earning her bachelor's degree in 1966.

Marriage to photographer and filmmaker Christopher Knight followed in 1971.

While pursuing a master's degree at Wheelock College, and with the encouragement of her parents and her husband, Lasky produced her first book, Agatha's Alphabet, a book for children which was published in 1975. Her next three books, also for children, were collaborations with her husband, who provided photographs for her texts: / Have Four Names...