Notable for young adult novels such as Something Rotten (2007), Fantasy Baseball (2011), Prisoner B-3087 (2013), and The Dragon Lantern: A League of Seven Novel (2015), Gratz is also recognized for his television writing work for the A&E series City Confidential. His 2017 novel Refugee was on the New York Times bestseller list for over two years.
After earning his bachelor's degree in Creative Writing and his master's degree in Education from the University of Tennessee, he published his debut young adult novel, Samurai Shortstop (2006).
In 2003, he was the co-recipient of the Society of Children's Book Writers and Illustrators' Kimberly Colen Memorial Grant.
He was born and raised in Knoxville, Tennessee, and he later settled in the western region of North Carolina.
In 2004, Gratz adapted Washington Irving's famous short story "The Legend of Sleepy Hollow" into a stage play that premiered at the Knoxville Actors Co-Op.