Corner was posted first to Washington in 1948, as First Secretary, where he was involved in the negotiation and signature of the ANZUS Treaty and the Japanese Peace Settlement. In 1952 he was appointed Deputy High Commissioner in London, and was in London during the Suez crisis when New Zealand found itself torn in its loyalties between its new friend and protector (the US) and its "mother country", Britain. In 1958, Corner returned to New Zealand as Deputy Secretary of Foreign Affairs.