At 19, Levithan received an internship at Scholastic Corporation where he began working on the The Baby-sitters Club series. Levithan still works for Scholastic as an editorial director. Levithan is also the founding editor of PUSH, a young-adult imprint of Scholastic Press focusing on new voices and new authors.
Levithan's first collaboration with author Rachel Cohn, 2006's Nick and Norah's Infinite Playlist was adapted for the big screen in 2008.