Dennis Letts was born in Oklahoma City on September 5, 1934. He grew up with his parents, Haskell and Hazel Letts, in Wagoner, Oklahoma. Letts graduated from Wagoner High School in 1952. He enlisted in the United States Air Force after graduation, where he served until 1956.
Letts received his bachelor's degree from Northeastern State University in Tahlequah, Oklahoma, thanks to the G.I. Bill. He went on to earn his master's degree from the University of Tulsa and his doctorate from the University of Illinois Urbana-Champaign. He also earned a Fulbright Scholarship.
Letts married his wife, novelist Billie Gipson, in 1958.
Letts spent much of his professional career as a writing and English professor. He taught for more than thirty years, mostly as a faculty member at Southeastern Oklahoma State University in Durant, Oklahoma.
Letts first began acting at the relatively late age of 50 years old. Letts first started performing at university and community theaters while still working as a college professor. He began acting as a full second career after retiring from teaching. Letts appeared in more than 40 films and television shows over the course of his career, including parts in high-profile films such as Cast Away in 2000.
His acting credits also included Where the Heart Is, a film based on a novel written by his wife, Billie Letts. Letts also served as an editor for his wife's novels, which have won various literary awards and have appeared on the the New York Times Best Seller list.
Dennis Letts originated the role of Beverly Weston in the original production of August: Osage County, which was written by his son, Tracy Letts. His character is described as an "Oklahoma patriarch" whose mysterious disappearance reunites his dysfunctional family. August: Osage County first opened at the Steppenwolf Theatre Company in the summer of 2007. The show, as well as Letts's performance, was a critical success.
Letts was diagnosed with lung cancer in September 2007. Despite his diagnosis, Letts chose to remain with the August: Osage County production as the show moved to New York City. The show, with Letts as a full cast member, debuted on Broadway in December 2007. It earned some of the best critical reviews of that particular season.
Dennis Letts continued performing eight shows a week of August: Osage County in New York City until February 2008. He kept up his schedule despite his illness and its treatment. Letts died in Tulsa, Oklahoma, on February 22, 2008, at the age of 73. A memorial service was held in Wagoner, Oklahoma.He was survived by his wife, Billie, and sons, Tracy, Dana and Shawn.