In 1979, Wickham played a leading role in calming political tensions after the assassination of South Korean President Park Chung Hee, and wrote a book Korea on the Brink about the dangerous period.

He also served as senior military assistant to Secretaries of Defense James R. Schlesinger and Donald Rumsfeld.

In 1983, president Ronald Reagan appointed Wickham Chief of Staff of the United States Army, the last Korean War-era veteran to be named to the post.

On 20 May, the same day that special-forces paratroopers shot protesters near Gwangju station, Wickham received a request from the ruling military junta to transfer OPCON for the ROK Army 20th division.

When asked to testify about the massacre in 1989 for the South Korean National Assembly, Wickham maintained that he had no way not to approve of the OPCON transfer.

He was named vice chairman for the United States-China National Committee and has served as a member of the Secretary of Defense Policy Board.

For the past 20 years he continues as the Military and Foreign Affairs speaker on The Buckmaster Show, KVOI radio in Tucson, Arizona.

In his autobiography My American Journey, General Colin Powell mentioned serving with Wickham and praised him as "every inch a Soldier".