Devenny was chosen as Minority Leader by the Liberal caucus of the Grand Council after the People's Coalition won a narrow majority in the 1938 Grand Council elections. He criticized Governor-General Hogg's economic policies, and was able to defeat Hogg's efforts to cut military spending.
After the German conquest of France and the Ottoman Empire in the Global War, Devenny and other members of the Liberal leadership supported Hogg's decision to provide military assistance to the British. Devenny accepted a Cabinet post in Hogg's wartime unity government; following Douglas Watson's retirement after the 1948 Grand Council elections, he became Minister for Foreign Affairs. By the time the unity government ended in November 1949 and Devenny resigned from the Cabinet, however, Councilman Richard Mason had become the leading figure in the Liberal Party. Following Hogg's stroke on September 16, 1950, Devenny joined other national leaders in the Executive Mansion, and was present at Hogg's death.
Sobel's source for Hugh Devenny's political career is Devenny's memoirs, War and Men: Politics in North America, 1943 - 1948 (New York, 1955).