He was born to a middle class family. At school, he was a very gifted student and was given a scholarship to study at Queen's College at Oxford. He entered that establishment in 1888, and got his Bachelor's degree in Jurisprudence in 1892. He got his D.C.L. from Oxford in 1901 and his LL.D. from Cambridge in 1903. His expertize was in the field of international law. He taught law at Nottingham, Oxford, London and Liverpool Universities. At that time, he became a prolific writer on international law.

Following the outbreak of the First World War, Baty took part in the establishment of the Hugo Grotius Society, established in London in 1915. As one of the original members of that society, Baty got to know Isaburo Yoshida, Second Secretary of the Japanese Embassy in London and an international law scholar from the graduate school of the Tokyo Imperial University. The Japanese government was searching at that time a foreign legal adviser following the death of Henry Willard Denison, a US citizen who served in that position until his death in 1914. Baty applied for that position in February 1915. The Japanese government accepted his application, and he came to Tokyo in May 1916 to start his work. In 1920 he was awarded the Imperial Order of the Sacred Treasure, 3rd grade, for his service as a legal adviser. He renewed his working contracts with the Japanese Ministry of Foreign Affairs several times, until in 1928 he became a permanent employee of that ministry. In 1936 he was awarded the Imperial Order of the Sacred Treasure, 2nd grade.

During his work for the Japanese government, Baty developed the notion that China was not worthy of recognition as a state under international law, a view that was later used to justify invasion of China.

In 1927, he was part of the Japanese delegation to the disarmament conference held in Geneva. This was his only public appearance as legal adviser to the Japanese government, as the rest of his work involved mainly writing legal opinions. In 1932, following the Japanese invasion of north China and the formation of Manchukuo, Baty defended the Japanese position in the League of Nations and called to accept the new state to league membership. He also wrote legal opinions in defense of the Japanese invasion of China in 1937.

In July 1941, the Japanese government froze the assets of foreigners residing in Japan or any of its colonial possessions in retaliation for the same move against Japanese assets in the US, but Baty was exempt from this due to his service for the Japanese government. Baty decided to remain in Japan even following the outbreak of war between that country and the British Empire in December 1941. He rejected the efforts by the British Embassy to repatriate him back to his country, and kept working for the Japanese government even during the war. He defended the Japanese policy of conquest as a remedy to western colonialism in Asia. In late 1944, he questioned the legitimacy of the pro-Allied governments established following the end of the German occupation in Belgium and France.

Following the Japanese surrender in 1945, the British Ministry of Foreign Affairs was considering indicting Baty for treason, but the Central Liaison Office (a British government agency operating in Japan) provided an opinion stating that Baty's involvement with the Japanese government during the war was insignificant. In addition, some legal advisers within the British government shielded Baty from possible prosecution on the grounds that he was too old to stand trial. Instead, the British government decided to revoke Baty's British nationality and leave him in Japan.

Baty's legal philosophy evolved as he worked for the Japanese government and was designed to justify Japanese actions of encroaching upon the sovereignty of China. His main argument was that the recognition of states must depend on one factor alone - effective control by the military and security forces of the government over the state's territory, and not on preconceived definitions of what the state should be. For that reason he opposed the procedure of according De Facto recognition, claiming that only final and irrevocable recognition must be used, and accusing the western international community of hypocrisy in using the de facto recognition as a means to allow some transactions with governments of states unfriendly to them without making the definite commitment to accept them fully into the family of nations.

Baty was never married. Some evidence suggests that he hated sex, as he was disillusioned with Victorian sexual norms, and was disgusted by the then accepted notions of male domination over female. An important female personality in his life was his sister, who went with him to Japan in 1916, and lived with him until her death in 1944.

Books

• International Law in South Africa (1900)
• International Law (1909)
• War: Its Conduct and Legal Results (New York: E. P. Dutton and Co. 1915) co-author with John H. Morgan
• The Canons of International Law (London: John Murray 1930)
• International Law in Twilight (Tokyo: Maruzen 1954)
• Alone in Japan (Tokyo: Maruzen, 1959), memoirs

Articles

• "Can an Anarchy be a State?" American Journal of International Law, Vol. 28, No. 3 (Jul., 1934), pp. 444-455
• "Abuse of Terms: 'Recognition': 'War' " American Journal of International Law, Vol. 30, No. 3 (Jul., 1936), pp. 377-399 (advocating the recognition of Manchukuo)
• "The 'Private International Law' of Japan" Monumenta Nipponica, Vol. 2, No. 2 (Jul., 1939), pp. 386-408
• "The Literary Introduction of Japan to Europe" Monumenta Nipponica, Vol. 7, No. 1/2 (1951), pp. 24-39, Vol. 8, No. 1/2 (1952), pp. 15-46, Vol. 9, No. 1/2 (1953), pp. 62-82 and Vol. 10, No. 1/2 (1954), pp. 65-80