After his father died, Gwaltney was raised in Charleston, Arkansas.

During World War II he served with the 112th Cavalry in the Philippines Campaign where he met Norman Mailer.

Returning to Arkansas after the war, Gwaltney obtained his high school diploma, then earned a degree in English from the University of Arkansas. He married Emma Carolyn Calhoun in 1947, earned a Masters in English in 1950 and taught at various schools.

He wrote his first novel The Yeller-Headed Summer with help of his war buddy, Norman Mailer. His most famous novel based on his war experiences was The Day the Century Ended that was filmed as Between Heaven and Hell.

Gwaltney wrote teleplays for Alfred Hitchcock Presents and The Fugitive.