Sidney Edward Mezes, professor, university president, and peace conference official for World War I, was born at Belmont, California, on September 23, 1863, the son of Simon Monserrate and Juliet Janin (Johnson) Mezes. His father was from northern Spain, and his mother was born in Italy; Mezes profited from these influences, as well as from extended visits in Europe, where he became a good linguist at an early age. He prepared for college at St. Matthew's Hall, San Mateo, California, and studied engineering at the University of California, where he graduated with a B.S. degree in 1884. After his father's death in 1884, Mezes managed the family's estate and took philosophy classes at the university. He entered Harvard in 1889 and received an A.B. degree in 1890, an M.A. degree in 1891, and a Ph.D. degree in 1893. He taught at Bryn Mawr College in 1892–93 and at the University of Chicago in 1893–94.
Mezes accepted a position as adjunct professor of philosophy at the University of Texas in 1894. He married Annie Olive Hunter, a sister-in-law of Edward M. House, on December 10, 1896; they had no children. Mezes rose quickly through the academic ranks, becoming associate professor in 1898, professor in 1900, dean of the College of Literature, Science, and Arts in 1902, and president in 1908. During his presidency the University of Texas added the Department of Extension, the Bureau of Economic Geology, and a new library; the number of students enrolled rose from 2,574 to about 3,000; and the legislature passed a law changing the terms of regents so that a governor could not name the entire board during one term in office. Mezes resigned the presidency at the end of 1914 and became president of the College of the City of New York. At the request of the board of regents he put in writing his views on the development of UT, published as The Future of the University of Texas (1914).
At CCNY, Mezes established the schools of technology, business, and education, and expanded the college's summer, evening, and vocational programs. He raised admission standards and academic requirements. He also helped establish the New York City board of higher education. Enrollment at CCNY rose from 5,200 in 1914 to roughly 20,000 by the time of Mezes's resignation in 1927.
In 1913 Mezes had declined the opportunity to become United States commissioner of education. In 1917, however, President Woodrow Wilson appointed him head of "the Inquiry," an organization to gather information for use at the Paris Conference at the end of World War I. The report of this commission provided the basis for Wilson's Fourteen Points. Mezes directed the section of territorial, economic, and political intelligence at the Paris Conference and also served as United States delegate to the Central Territorial Commission. He received honorary LL.D. degrees from Southwestern University in 1912, the University of California in 1913, and New York University and the University of Cincinnati in 1915; the University of Texas at Austin made him president emeritus in 1929. He coauthored The Conception of God (1898), wrote Ethics, Descriptive and Explanatory (1901), and contributed to What Really Happened at Paris, edited by C. Seymour and E. M. House (1921). Mezes resigned from CCNY in 1927 in ill health. He spent most of the rest of his life in Arizona, California, and Europe. He died at Altadena, California, on September 10, 1931. Mezes Hall on the University of Texas campus was dedicated in his honor in April 1953.