At 15 Carson ran away from his home in Missouri to join a caravan of traders bound for Santa Fe. From experienced frontiersmen he learned fur trapping and trading, a career he pursued for 15 years.

A chance encounter in 1842 with the explorer John C. Frémont (Frémont, John C) made Carson an active participant in the clash of empires that eventually extended the boundaries of the continental United States to its present size (Alaska excluded). He served as a guide to Frémont's government-financed explorations of the West in 1842 and 1843–44, and he was with him in California at the conclusion of the third expedition in 1846, when Frémont provoked the uprising generally known as the Bear Flag Revolt. En route to Washington, D.C., carrying dispatches from Frémont, Carson met Gen. Stephen W. Kearny, who pressed him into service as a guide for his command headed for California with presidential orders to take over the region for the United States. From then until the end of the war with Mexico (1848), Carson alternated fighting and guiding with dispatch-bearing to Washington, where his reputation for bravery, loyalty, and devotion to duty won for him many friends in high office.

In 1854 Carson, who had been married to an Arapaho woman and a Cheyenne woman, became a reputedly sympathetic Indian agent at Taos for the Ute. But by 1861 he was back in the field to serve the cause of the Union in the U.S. Civil War in the Southwest, becoming Colonel Carson of the 1st New Mexico Volunteers. In 1863 he received orders to subdue the Navajo, who were fighting for control of their traditional lands. Aided by the Navajo's enemies, including the Ute, Hopi, and Zuni, Carson oversaw the widespread destruction of the tribe's homes, crops, and livestock. The Navajo surrendered in 1864, and Carson subsequently ordered some 8,000 Navajo on a 300-mile (480-km) forced march, known as the Long Walk, to Bosque Redondo, a piece of land south of Sante Fe in New Mexico Territory ill-suited to the agriculture the Navajo had practiced in their native Canyon de Chelly. Carson's last major battle occurred at Adobe Walls, a trading post in the Texas Panhandle, in November 1864. He led a force of some 300 volunteers to a draw against several thousand Kiowa and Comanche before ordering a withdrawal. In January 1868 he was appointed superintendent of Indian affairs for Colorado Territory, a position he held at the time of his death.

Carson's name is preserved variously throughout the Southwest, including Nevada's capital at Carson City; Ft. Carson, Colo.; and Carson Pass in California.