In January 1998, Kinney brought up the idea of a middle-school weakling named Greg Heffley, who writes illustrated stories about his personal life. In May 2004, FunBrain and Jeff Kinney released an online version of the story, titled Diary of a Wimpy Kid. The website made daily entries until June 2005. He worked on his book for almost eight years, before showing it to a publisher in New York.

In February 2006, during the New York Comic Con, Jeff signed a multi-book deal with publisher Harry N. Abrams, Inc., to turn Diary of a Wimpy Kid into a print series.

The book became an instant hit, with the online version receiving about 20 million views as of 2007. When many online readers requested a printed version, Kinney agreed, and in April 2007, Diary of a Wimpy Kid was published. To date, fourteen Wimpy Kid books have been released, including a do-it-yourself book and a movie diary. In April 2009, TIME named Kinney one of The World's Most Influential People. In 2016, the series won a Nickelodeon Kids Choice Award for Favorite Book.