Humes was born in Philadelphia and attended Hampshire College in Amherst, Massachusetts. In 1985 he moved to Southern California.
In 1989 he received the Pulitzer Prize for specialized reporting for several investigative stories he wrote about the United States military. Afterwards, he began writing non-fiction books.
In 2001, Humes spent a year teaching a writing workshop at Whitney High School in Cerritos, California, a middle-class Los Angeles suburb. His observations while at the school led to his much-applauded narrative non-fiction book School of Dreams, published in 2004.
Since 2001, Humes has worked as a writer for Los Angeles magazine.