He was one of the civilian Promoters of the Siamese Revolution of 1932 that changed the country's form of government from absolute to constitutional monarchy. He was closely associated with Pridi Banomyong. In the government of Field Marshal Plaek Phibunsongkhram he served as Minister of Foreign Affairs, but resigned when Phibunsongkhram led Thailand into World War II alongside Japan. Direk became a member of the Free Thai Movement (Seri Thai) alongside Pridi, who fought for the full sovereignty of Thailand and against collaboration with Japan. After the end of war, he served as Minister of Justice, Finance, Foreign Affairs and Deputy Prime Minister in several short-lived cabinets. From 1949 to 1952 he was the first dean of the Faculty of Political Science, Thammasat University.
Direk served in many important posts in the Thai government during the early years of constitutional rule. During World War II, he held the post of Foreign Minister to become the Ambassador to Japan. He also held the posts of Deputy Prime Minister, Foreign Minister (multiple times), Justice Minister, and Finance Minister. He also served as the Thai Ambassador to the Court of St. James's (England), Germany and Finland.
Direk's younger brother was Pairote Jayanama, former Permanent Secretary of Foreign Affairs (who had 4 sons who eventually became ambassadors), and AM Jayanama, an Air Force General at the time.
He was married to Khunying ML Pui, member of the aristocratic Nopawongse royal bloodline, and had 4 sons with her. One son, Wattana Jayanama, became an important figure during the establishment phase of the Bank of Thailand.
- Direk Jayanama. Thailand and World War II (2008) 575pp;