He worked on "The Simpsons" as a writer and producer until 2003, and later contributed to "The Simpsons Movie". He wrote the largest number of "Simpsons" episodes (59 full episodes, with contributions to several others) by a large margin. After his retirement from the show, he began a career as a writer of self-published absurdist novels. He has written more than eleven novels, the most recent of which, "The Squirrel Who Saved Practically Everybody", was published in 2019. In November 2020, Swartzwelder announced that he would release another book, "The Spy With No Pants", in December of that year.