George Brinton McClellan, United States army officer, engineer, and politician, was born in Philadelphia, Pennsylvania, on December 3, 1826, the son of Dr. George and Elizabeth Steinmetz (Brinton) McClellan. After attending the University of Pennsylvania he entered the United States Military Academy at West Point on July 1, 1842, and graduated second in his class in 1846. He was brevetted a second lieutenant in the Corps of Engineers and, as a member of Maj. Gen. Winfield Scott's staff, won brevets to first lieutenant and captain for distinguished service in the Mexican War. He took part in the battles of Contreras, Churubusco, and Chapultepec. For the three years following the war he was an instructor at West Point. In June 1851 he was transferred to assist in the construction of Fort Delaware, on an island in the Delaware River some forty miles below Philadelphia. Less than a year later, however, he was appointed engineer, commissary, quartermaster, and second-in-command of Capt. Randolph B. Marcy's Red River expedition. On March 5, 1852, McClellan was ordered to Fort Smith, Arkansas. From there the seventy-five-man expedition moved to Fort Washita, Indian Territory, and then into the Texas Panhandle. In 1852 the upper Red River area remained the largest unexplored tract of Texas, and the expedition's duty was to map the region for future travelers and settlers. Also among McClellan's duties was the keeping of a detailed daily meteorological record and a collection of mineral samples found on the route. On June 16 the party discovered the source of the north fork of the Red River and named it McClellan Creek. Of the Palo Duro Canyon McClellan wrote, "the scenery equals in beauty and wildness any that I ever beheld. The immense bluffs tower above us on every side, and assume every shape that fancy may suggest." McClellan married Marcy's daughter Mary Ellen on May 22, 1860, and they had two children.
Back in Arkansas on July 28, McClellan received orders to report to Brig. Gen. Persifor F. Smith, commander of the Military District of Texas. As Smith's chief of engineers, McClellan accompanied the general on tours of inspection of frontier forts in Texas. In October 1852 he was ordered to oversee a survey of the state's rivers and harbors from headquarters at Corpus Christi, and in March 1853 he reported the need for extensive dredging of port facilities. In April he was assigned to a surveying expedition for a proposed railroad through Washington Territory to the Pacific Ocean. He was promoted to captain and assigned to the First United States Cavalry on March 3, 1855, and that same month Secretary of War Jefferson Davis sent him to Russia to observe French and English military operations in the Crimean War. When he returned from Europe he designed the famous cavalry saddle that still bears his name. He resigned from the army in 1857 and became chief engineer and later vice president of the Illinois Central railroad; in 1860 he became president of the Ohio and Mississippi railroad.
In 1861 McClellan was living in Cincinnati. On April 23, with the outbreak of the Civil War, the governor appointed him a major general of Ohio volunteers. His victories at Rich Mountain and Corrick's Ford, now in West Virginia, won him national attention, and on July 27, 1861, President Abraham Lincoln appointed him commander of the principal Union army in the East, which McClellan reorganized and named the Army of the Potomac. A staunch Democrat, he quarreled bitterly with Lincoln and many of his cabinet, but nevertheless, on November 1, 1861, he was named general in chief of all United States forces. Only after receiving a direct order from Lincoln did he launch his amphibious invasion of Virginia in March 1862, landing his 118,000-man army at Fort Monroe on the tip of the peninsula formed by the James and York rivers. His march up the peninsula toward Richmond was repeatedly checked by much smaller Confederate forces under generals John B. Magruder and Joseph E. Johnston, and in a series of battles around the Confederate capital in late June McClellan was repulsed by Gen. Robert E. Lee and forced to withdraw his army to its transports and sail for Washington. Lincoln, disgusted with McClellan's failures, relieved him of his duties as general in chief in July 1862 and transferred most of his divisions to Maj. Gen. John Pope's Army of Virginia. But when Lee delivered Pope a resounding defeat at the second battle of Manassas or Second Bull Run, McClellan was restored to command of his army. He fought a drawn battle with Lee's weaker Army of Northern Virginia at Sharpsburg, Maryland, (also known as the battle of Antietam) on September 17, 1862, but failed to exploit his strategic advantage. Lincoln therefore removed him from command for a second and final time.
McClellan thereupon entered politics full-time and in 1864 ran as the Democratic candidate for president of the United States. He resigned from the army on election day, November 8. After his defeat he returned to civil engineering and from 1878 until 1881 served as governor of New Jersey. In August 1885 he and Marcy returned to the Red River to inspect a Foard County copper-mining venture that McClellan had organized. His autobiography, McClellan's Own Story, published in 1887, is generally considered acutely biased and self-serving. He died in Maywood, New Jersey, on October 29, 1885, and was buried in Riverview Cemetery, Trenton.