Spanish writer, diplomat, and historian, noted for his service at the League of Nations and for his prolific writing in English, German, and French, as well as Spanish.

The son of a Spanish army officer, Madariaga was trained at his father's insistence as an engineer in Paris but abandoned his career to become a journalist. In 1921 he joined the Secretariat of the League of Nations at Geneva as a press member and the following year was appointed head of its disarmament section. From 1928 to 1931 he was professor of Spanish studies at the University of Oxford. After the Spanish monarchy fell in 1931, the Spanish republic appointed him ambassador to the United States (1931) and then to France (1932–34), and he was Spain's permanent delegate to the League of Nations from 1931 to 1936. When the Spanish Civil War broke out in July 1936, Madariaga—“equally distant from both sides,” as he wrote at the time—resigned and left for England. He became a vocal opponent of the Francisco Franco regime and did not return to Spain until April 1976, following Franco's death the previous November.

Among Madariaga's most notable essays are Englishmen, Frenchmen, Spaniards (1928), a study of national psychology; Guía del lector del Quijote (1926; Don Quixote), an analysis of Cervantes' classic; and Spain (1942), a historical essay. He also published books on various periods in Latin-American history, among them Cuadro histórico de las Indias, 2 vol. (1945; The Rise and Fall of the Spanish American Empire), and the trilogy Christopher Columbus (1939), Hernán Cortés (1941), and Simón Bolívar (1949), the last being the object of violent criticism for its iconoclasm. Madariaga's political writings expound his philosophy of individual liberty and the solidarity of mankind.

In addition to the essay, Madariaga cultivated other literary genres—poetry, drama, and narrative prose. His novels are based upon philosophical, political, and religious themes. Among his fictional works are El corazón de piedra verde (1942; The Heart of Jade) and Guerra en la sangre (1957; War in the Blood), novels based on Latin-American history.