During 21 years of federal service, Addington worked at the CIA, the Reagan White House, the Department of Defense, four congressional committees, and the Cheney Office of the Vice President. He was appointed to replace I. Lewis "Scooter" Libby Jr. as Cheney's chief of staff upon Libby's resignation when Libby was indicted on charges of perjury and obstruction of justice on October 28, 2005. Addington was described by U.S. News & World Report as "the most powerful man you've never heard of" in May 2006.
Addington is the son of Eleanore and the late Jerry Addington, a retired brigadier general and West Point graduate. He is married to Cynthia Mary Addington; the couple have three children. Previously, Addington had been married to Linda Werling, whom he met while the two were both attending Duke University.