He led a delegation from the organization to West Africa in 1963, and served as a member of the United States National Commission for UNESCO.

On November 15, 1964, twelve days after his election victory, Johnson appeared on the CBS Television Network quiz show What's My Line?

He was also a consultant to the U.S. Senate Select Committee on Presidential Campaign Activities in 1973.

He resided in Alexandria, Virginia, and served as executive director of the United States Association of Former Members of Congress from 1974 until his death.

Johnson died in Falls Church, Virginia, on December 16, 1993, as the result of a cerebral aneurysm.