Runnels attended Dallas public schools and Cameron State Agricultural College (now Cemeron University) in Lawton, Oklahoma. He was employed by the Federal Bureau of Investigation in Washington, D.C., in 1942.
Runnels' educational path included attending Dallas's public schools and later studying at Cameron State Agricultural College (now known as Cemeron University) in Lawton, Oklahoma. In 1942, he embarked on a career with the Federal Bureau of Investigation in Washington, D.C.