By 1962 Bridwell was married to his wife Norma, and they had an infant daughter Emily Elizabeth. Bridwell put together a portfolio and attempted to get a job as an children's book illustrator but was rejected by around fifteen publishing houses. While at Harper & Row, an editor offhandedly suggested he turn one of his drawings into a story. The drawing was of a baby girl and a horse-sized bloodhound, and the story became Clifford The Big Red Dog. That book spawned over 40 best-selling Clifford books, two television series, merchandise, and a live musical.
Bridwell's other successful books include The Witch Next Door, and A Tiny Family. There are over 126 million copies of his books in print in 13 languages.