Hess previously performed with The Black Crowes, Joan Osborne and Freedy Johnston, and, most recently, toured with The John Scofield Band.
"We've been fortunate to have many amazing bass players tour and record with us," guitarist Warren Haynes said. "When we played with Andy Hess -- it felt like a band."
Hess has played and recorded with Gov't Mule numerous times over the past three years.
"It's a real honor and privilege to play with Gov't Mule," said Hess. "Allen's are some big shoes to fill, but I am going to try to put my own stamp on it. I am very excited about being a part the band."
ATO Records will release Gov't Mule's latest offering, "The Deepest End," Oct. 7, as a bundled DVD and two CD package that will include 32 songs from the May 3, 2003, Saenger Theater concert.