Kathryn Lasky grew up in the suburbs of Indianapolis, Indiana, with her father, her mother, and her big sister, Martha. She attended the University of Michigan and majored in English, becoming particularly interested in Victorian literature, Romanticism, and the Renaissance. After graduating, Lasky began working as a writer for a fashion magazine, though she later opted for a career as a teacher. While teaching, she met and married Christopher Knight, a National Geographic photographer and documentary filmmaker. Lasky began writing children's books after returning from her second voyage across the Atlantic Ocean with her husband. She has since written many books for children, including fiction, nonfiction, and picture books, as well as several books for adults.

Kathryn Lasky has two children and cites her family as the most important inspiration for her books, including Newton's Rainbow. She lives with her husband in Cambridge, Massachusetts.