Harrow School; New College.
In 1909 he published Spain, a Study of her Life and Arts, the first work in English to recognize the genius of El Greco. Appointed by the British government to edit the Calendar of State Papers related to negotiations between England and Spain in the time of Charles V, Holy Roman Emperor, he published the first of the five volumes of these papers in 1913. The last, completed just before his death, appeared in 1954.
During World War I he served as an officer in the United States Army.
In 1919 he joined the United States delegation to the Paris Peace Conference, and in 1924 the League of Nations appointed him Financial Advisor to the government of Hungary. With Hayford Peirce (the older brother of the painter Waldo Peirce) he published in French a pioneering study of Byzantine art, and he died just after completing his posthumously published biography, The Emperor Charles the Fifth.
Tyler also helped to inspire and shape the major collections of Pre-Columbian art and Byzantine art brought together by Robert Woods Bliss and Mildred Barnes Bliss and housed at Dumbarton Oaks in Washington, District of Columbia. He spent most of World World War II in Geneva, Switzerland, where he drew on his high-level, Europe-wide connections to perform vital work for the United States intelligence network run by Allen Welsh Dulles. He spent his last years in Paris, first with the International Bank for Reconstruction and Development, then as European Representative of the National Committee for a Free Europe.