Kinney works full-time as a writer and designer of online games. According to his website, he also created the kid-friendly website Poptropica. Poptrica is known by many children around the world. Kinney grew up in Fort Washington, Maryland, United States, not far from Crossland High School, and attended the University of Maryland at College Park in the early 1990s. It was in college that Kinney created the popular comic strip Igdoof that ran in the campus newspaper, The Diamondback. While there, he knew that he wanted to be a cartoonist. However, Kinney was not successful in getting his comic strip syndicated after college, and in 1998, he started writing his ideas which would eventually become Diary of a Wimpy Kid. The series has 40 million copies in print world wide as of 2010 and was developed into a feature film, for which Kinney also served as an executive producer.

To date, four Wimpy Kid books have been released, plus a do-it-yourself book. At least one additional book is planned to be released in November 2010.

In 2009, Kinney was named one of Time magazine's 100 "Most Influential People" in the world.

Kinney grew up with two brothers and a sister and attended Bishop McNamara High School in Forestville, Maryland. Kinney currently lives in Plainville, Massachusetts with his two sons, Will and Grant, and his wife.

On July 22, 2009, Fox 2000 announced that Zachary Gordon would star in a film adaptation of Kinney's Diary of a Wimpy Kid series of books. The original release date was April 2, 2010, but the release was moved up to a March 19, 2010 US release.