Educated at Dartmouth College, Hanover, N.H., Marsh developed a successful law practice, but his wide-ranging mind led him into the study of classical literature, languages (he was fluent in 20 by the age of 30), and the applied sciences of silviculture and soil conservation. In 1842 he was elected to Congress, where he was greatly influenced by former president John Quincy Adams, a fellow congressman whose foresight and ideas of government's role in natural resource preservation and management anticipated those of Theodore Roosevelt. After serving a second term in Congress, Marsh was appointed minister to Turkey by Pres. Zachary Taylor, during which assignment he studied Middle Eastern and Mediterranean geography and agricultural practices. He sent many specimens to the Smithsonian Institution in Washington, D.C., before his recall in 1852. Marsh was a lecturer in English philology and etymology at Columbia University and the Lowell (Mass.) Institute. He became a member of the Republican Party in 1856. In 1861 Pres. Abraham Lincoln made him the first minister to Italy, a position he held until his death. During that period he summarized his accumulated knowledge and experience in Man and Nature, or Physical Geography as Modified by Human Action (1864).