A West Point Military Academy graduate, Reno fought in the American Civil War and achieved the rank of major.

After the war Reno served with George Armstrong Custer's 7th Cavalry. At the Battle of the Little Bighorn, Reno commanded the only unit to survive. Many people refused to believe that Sioux Indians alone could have defeated Custer, and suggested that Reno's behaviour during the battle might have been less than exemplary. An 1879 court-martial acquitted him of the charge of cowardice.

The following year, an officer, whose own son had died at the Little Bighorn, accused Reno of drunkenness and disorderly conduct in an unrelated incident. This time, Reno was found guilty and dishonourably discharged.

When he died in 1889, Reno's family wanted to bury his body at the Little Bighorn. The U.S. Army denied the request. In 1967, a military board of review reversed the 1880 decision and changed Reno's discharge status to honourable. His remains were disinterred and reburied in the Little Bighorn cemetery.