Born in Elora, Tennessee, Hefner graduated from high school in Sardis, Alabama. He attended the University of Alabama, and he became the president and owner of radio station WRKB in Kannapolis, North Carolina.
In 1974, he was elected as a Democrat to the 94th United States Congress. He served a total of 12 terms, from January 3, 1975 until January 3, 1999, when he retired from Congress. Hefner built a reputation as an advocate for military veterans, and the Veterans Affairs Medical Center in Salisbury, North Carolina, was renamed in his honor on April 16, 1999.
He served from October 2001 until November 2002 as the District One commissioner for Marshall County, Alabama.
He died in Huntsville, Alabama on September 2, 2009 after suffering a brain aneurysm.
He was a member of the Harvesters Quartet, a group of gospel music singers based in North Carolina, from 1954 to 1967, and was a television performer on numerous North Carolina television channels.
Married Nancy Louise Hill, March 23, 1952. Children: Stacye, Shelly.