After serving in World War I, Hoare returned to parliament and became one of the principal Conservatives who revolted against continued participation in the Lloyd George government in 1922. He was rewarded with the position of Secretary of State for Air, which he held in all the various Conservative governments of the 1920s.
When the Conservatives joined the National Government in 1931, Hoare became Secretary of State for India in which capacity he negotiated, with great difficulty, the passage of the landmark Government of India Act 1935. He was, however, most famous for his activities as Foreign Secretary beginning in 1935. In 1935, Hoare was instrumental in obtaining approval for the British rescue effort on behalf of endangered Jewish children in Europe known as the Kindertransport.
In the same year, Hoare dealt with the Italian invasion of Ethiopia. Together with French Foreign Minister Pierre Laval, he developed the so-called Hoare-Laval Agreement, which would have granted Italy considerable territorial concessions in Ethiopia, and put the rump of Ethiopia under Italian hegemony. The public uproar against this apparent sell-out of the Ethiopians led to Hoare's resignation as Foreign Secretary at the end of the year. His successor was Anthony Eden. When Eden had his first audience with King George V, the King is said to have remarked "No more coals to Newcastle, no more Hoares to Paris."
Nevertheless, Hoare continued to serve in important posts in later governments. Upon Winston Churchill's appointment as Prime Minister in 1940, Hoare lost his cabinet position and was sent off as Ambassador to Spain, with his wife Lady Maud Hoare. In this role he sought to encourage Francisco Franco to keep Spain out of the war, in which he was successful. He remained Ambassador until 1944 when he returned to Britain and was raised to the peerage as Viscount Templewood, of Chelsea in the County of Middlesex. The baronetcy and peerage became extinct upon his death in 1959.