Mo Willems, the son of Dutch immigrants, grew up in New Orleans. He spent much of his youth telling stories and drawing. Willems especially loved reading "Peanuts" comics and then sketching Snoopy and Charlie Brown himself. "I even wrote a letter to Charles Schulz," Willems recalls, "saying that I wanted his job when he died." During high school, Willems acted in plays and started doing standup routines at comedy clubs.

After high school, Willems traveled abroad and performed standup comedy in London. He later moved to New York, where he studied film and then switched to animation. Willems spent the first part of his career writing and animating for children's television. For nine years, he worked on Sesame Street, where he won six Emmy Awards and developed characters such as Suzy Kabloozie. Willems later created “Sheep in the Big City” for the Cartoon Network and “The Off-Beats” for Nickelodeon.

For five years, Willems tried to write and illustrate children's books. After a number of rejections, Willems' simple doodle of a pigeon attracted the eye of an editor. This pigeon would become the star of his first book, Don't Let the Pigeon Drive the Bus, which won a Caldecott Honor in 2004. The following year, Knuffle Bunny won another Caldecott Honor, which further solidified Willems' new career as a children's book author and illustrator.

Willems is best known for his Caldecott Honor winning picture books Don’t Let the Pigeon Drive the Bus!, Knuffle Bunny: a Cautionary Tale, and Knuffle Bunny Too: a Case of Mistaken Identity. In addition to such picture books as Leonardo the Terrible Monster, Edwina the Dinosaur Who Didn’t Know She Was Extinct, and Time to Pee!, Mo created the Theodor Seuss Geisel Medal winning Elephant and Piggie books, a series of early readers, and published You Can Never Find a Rickshaw When it Monsoons, an annotated cartoon journal sketched during a year-long voyage around the world in 1990-1991.

His picture books have been translated into a myriad of languages, spawned Carnegie Medal winning animated shorts, and theatrical musical productions. His illustrations, wire sculpture, and carved ceramics have been exhibited in galleries and museums across the nation.

Mo Willems writes and illustrates from his home in Brooklyn, New York, where he lives with his wife and daughter.