Martin graduated from the University of Indiana in 1846 and from New Albany (Indiana) Theological Seminary (later relocated to Chicago and renamed McCormick Theological Seminary) in 1849. In 1850 he and his wife, the former Jan VanSant, went to Ningpo (Ningbo), China, one of the five treaty ports opened to foreign residence by the Treaty of Nanking in 1842. During ten years of general missionary service in this south China port city, Martin involved himself in two major events of Chinese history. First, he went on public record to advocate to his government in four newspaper articles that it should support the Taiping Heavenly Kingdom, a large-scale revolt against the reigning Manchu government. Second, he participated actively in the American delegation that produced the Treaty of Tientsin, the second of unequal treaties between China and the Western powers, which opened the entire country to traders, diplomats, and missionaries.
After a short transition period of one year in Shanghai, Martin moved to Peking (Beijing) in 1863, and with an interruption of only three or four years, remained there until his death. During 25 of these years in Peking, although he continued to think of himself as a missionary, he worked primarily as a teacher, administrator; and translator in the government-sponsored Tong Wen Kuan (Interpreters' school), in the new Imperial University in Peking, and in a school in Wuchang, Hupei (Hubei) Province, in central China. He also filled many other roles. He was editor of Peking Magazine, an early Chinese reform magazine; special correspondent for the New York Times; adviser to the Chinese government on education and international politics; reformer; Bible translator; and author. The last ten years of his life in Peking were spent as an honorary missionary with the American Presbyterian Board.
Martin was widely acclaimed for his writings in both Chinese and English. His major Chinese book, Tiantao Suyuan (Evidences of Christianity), was recognized by the 1907 Centennial Missionary Conference as the single best Christian book of the century. He also wrote Tiantao Hechiao (Christianity and other creeds) and a seven-volume work, Kown jumen (Natural philosophy). He translated into Chinese the well-known work Elements of International Law by Henry Eaton. His best-known works in English are A Cycle of Cathay (3d ed., 1900), Siege in Peking (1900), and The Lore of Cathay (2d ed., 1912).