Harold Leon Breeden was born on October 3, 1921, in Guthrie, Oklahoma. When he was three years old, his family moved to Wichita Falls, Texas, where he spent the remainder of his childhood and graduated from Wichita Falls High School in 1939. Breeden initially attended Texas Wesleyan College, and transferred to Texas Christian University. During the Second World War, he served in the U.S. Army's 69th Infantry Division, stationed at Fort Bliss. He earned both a Bachelor of Arts in music (1945) and a Master of Music Education degree (1948) at TCU, where he served as a band director from 1944 through 1949. He then did coursework toward a Ph.D. at Columbia University in New York City. While in New York, he worked as an arranging assistant to Don Gillis, who was the producer for the NBC Symphony Orchestra under Arturo Toscanini. Breeden wrote arrangements for Arthur Fiedler of the Boston Pops, who offered him a full-time position. However, Breeden's father was in poor health, and Breeden returned to Texas to care for him.
After returning to Texas, Breeden resumed performing in local jazz bands, and worked as an arranger for WBAP-TV in Fort Worth (now KXAS). In 1953, Breeden became the band director at Grand Prairie High School, and succeeded Gene Hall as director of lab bands at what is now the University of North Texas in 1959, when Hall took a job at Michigan State University.
Under Breeden, jazz studies expanded at North Texas, and the One O'Clock Lab Band rose in stature both nationally and internationally, though "stage band" camps, airplay on Willis Conover's Jazz Hour on the Voice of America, a State Department-sponsored tour of Mexico, and performing at the White House. Breeden persevered through personal tragedy, with the loss of his son Danny in a hit-and-run car accident in 1968, and in the 1970s, the Lab Band received Grammy nominations, and toured in western Europe and the Soviet Union. Breeden retired from directing the Land Band in 1981, but continued teaching until 1984. He remained active as a clarinetist and public speaker. Leon Breeden died on August 11, 2010, in Dallas.