Stiles also wrote for periodicals, authoring pieces for Smithsonian, Denver Post, and the Los Angeles Times.

Stiles argued that Jesse James won political support by depicting himself as a Confederate avenger after the Civil War, as opposed to the traditional notion that he was an anti-railroad Robin Hood figure.

[6] In 2009, after seven years of work, Stiles published his second biography The First Tycoon: The Epic Life of Cornelius Vanderbilt (New York: Alfred A. Knopf, 2009).

[6] Stiles next released a biography of George Armstrong Custer, Custer's Trials: A Life on the Frontier of a New America (New York: Alfred A. Knopf, 2015), a study of the popular federal cavalry general in the American Civil War who famously died at the hands of Lakota, Cheyenne, and allied Native American forces in 1876.

"[10] Thomas Powers remarked in the New York Review of Books that Stiles's relegation of the Battle of Little Bighorn to the epilogue "is about the boldest purely literary decision I’ve seen in a long while, and the effect is startling.

From 2004 to 2005, Stiles held the Gilder Lehrman Fellowship in American History at the Dorothy and Lewis B. Cullman Center for Scholars and Writers at the New York Public Library.

He served as a consultant and on-screen interview subject in the PBS series The American Experience, for the films Jesse James and Grand Central, among other programs.

He also taught nonfiction creative writing at Columbia University, and belonged to the faculty of the 2014 World Economic Forum annual meetings.