In 1974, Wachtmeister was appointed ambassador in Washington, D.C. and eventually became Dean of the Diplomatic Corps. Wachtmeister's predecessor as Dean of the Diplomatic Corps was the Soviet Union's ambassador, which led Wachtmeister to famously quip that this was the first time that a Count had succeeded a communist. Despite being the Swedish Ambassador during a period of turbulent U.S.-Swedish relations engendered by Swedish opposition to the Vietnam War and soon-to-be Prime Minister Olof Palme's declaration that President Richard Nixon was a war criminal for his decision to bomb Cambodia, Wachtmeister managed to forge good relations with successive U.S. Presidential administrations, and even became the first President Bush's favorite tennis partner.