Nathaniel Michler, army officer and geographer, the son of Peter S. and Elizabeth (Hart) Michler, was born on September 13, 1827, at Easton, Pennsylvania. He attended Lafayette College before his appointment to the United States Military Academy, West Point, New York, on July 1, 1844. He graduated seventh in his class in 1848, and was brevetted second lieutenant, Topographical Engineers, on July 1, 1848, and assigned to Corpus Christi, Texas. He established a camp on the Mission River near Refugio, where he trained his men in surveying and tactics to employ against the Indians. His reconnaissance of the country between Corpus Christi and Uvalde was considered a model of geographic exploration on its issue in 1849. From 1851 to 1857 he worked on the Mexican boundary survey; his reports on that work may be found in William H. Emory's Report on the United States and Mexican Boundary Survey (1857, 1859). Michler was promoted to second lieutenant in 1854 and first lieutenant in 1856, and from 1857 to 1860 he served as chief topographical engineer in surveys for a canal from the Gulf of Darien to the Pacific Ocean. He was recalled in 1858 to establish the boundary between Maryland and Virginia, but returned to Panama in 1859 to complete the canal project. He was made captain in 1861 and served with the armies of the Ohio and Cumberland, 1861–63. At the specific request of the commanding general, he was transferred to the Army of the Potomac in order to resurvey Harper's Ferry. He and his men prepared detailed reconnaissances and built defensive works in the battles of the Wilderness, Spotsylvania, Cold Harbor, and Petersburg. He became a major of the Corps of Engineers in 1864, then on August 1, 1864, was brevetted lieutenant colonel for "faithful and meritorious service in the field." On April 2, 1865, he was brevetted colonel for his service during the siege of Petersburg, Virginia, and brigadier general for his services during the Civil War.
Michler was chosen in 1866 to select a site for a presidential mansion and public park in Washington. From 1866 to 1871 he helped prepare plans for a new War Department building. He was superintendent of public buildings and grounds in the District of Columbia until 1871 and also during this time was in charge of surveying the Potomac River and making repairs on Fort Foote, Maryland. In 1871–72 he was chief engineer with the General Commanding Division of the Pacific. From 1872 to 1875 he was engineer for several lighthouse districts and supervisor of a number of harbor and river improvement projects. Around this time he elicited great interest in his proposal for a canal between Coos Bay, Oregon, and the Coquille River. He superintended river and harbor improvements on Lake Erie, 1876–78, and from 1878 to 1880 served as military attaché for the United States Legation in Vienna, Austria. He was superintending engineer for river and harbor improvements for the states of New York, New Jersey, and Vermont in 1880 and 1881.
He was married to Fannie Kirkland shortly after graduating from West Point. Fannie died in 1857, and Michler married Sallie A. Hollingsworth in San Francisco on February 12, 1861; Sallie survived him. Michler died of Bright's disease on July 17, 1881, at Saratoga Springs, New York, and was buried at Easton, Pennsylvania.