President of the United States Lyndon B. Johnson nominated Green as United States Ambassador to Indonesia on June 4, 1965, and Green presented his credentials to the Indonesian government on July 26, 1965. He was met with an anti-Vietnam War protest organized by Sukarno, the President of Indonesia, under the slogan "Go Home, Green". Only weeks later, Green witnessed first hand the Transition to the New Order, an anti-communist purge in which Suharto led a coup against Sukarno following the murder of six generals by the 30 September Movement, which was blamed on the PKI by the Indonesian military based on dubious evidence. Green supported the Indonesian Army's version of the events, but contemporary historians have challenged it, with historian Geoffrey B. Robinson of UCLA in particular noting that Green and other US officials involved in supporting the Suharto coup "published memoirs and articles that sought to divert attention from any possible US role, while questioning the integrity and political loyalties of scholars who disagreed with them." An estimated 500,000 to one million Indonesians were killed in the massacres that followed. Recent revelations from government archives confirm that Green himself endorsed the Indonesian military "destroying PKI" through executions, noting in an October 20, 1965 telegram that he had "increasing respect for its determination and organization in carrying out this crucial assignment." According to Mark Aarons, he is "seen as one of the principal officials involved in encouraging the slaughter." Green was Ambassador to Indonesia until March 26, 1969; during his four years in Indonesia, he practiced what he called "low-profile diplomacy".