Ambrose Everett Burnside was born May 23, 1824, near Liberty, Indiana, and finished near the middle of his class at the U.S. Military Academy at West Point in 1847. After serving garrison duty in the Mexican War (1846–1848) and two years on the western frontier, he resigned his commission in 1853, settled in Rhode Island, and was issued a patent for the breech-loading Burnside carbine. The weapon, however, proved popular only after Burnside had gone bankrupt attempting to manufacture it. While treasurer of the Illinois Central Railroad, he worked for McClellan, a friend from West Point.

Burnside began his service in the Civil War as colonel of the 1st Rhode Island Infantry, but after the First Battle of Manassas (1861), he was made a brigadier general. In charge of what would later become the Army of the Potomac's Ninth Corps, he battled gale-force winds, seasickness, and knee-deep swamps to seize and occupy Roanoke Island and the North Carolina sounds, victories that helped to solidify the Union navy's blockade of the Atlantic coast.

Several months later, in July 1862, Burnside's corps joined the Army of the Potomac and, after Second Manassas, he refused command of the army for the second time, partly out of loyalty to his old friend McClellan. At the Battle of Antietam on September 17, Burnside's supposed delay in attacking from the left flank infuriated McClellan. (In fact, McClellan tried to excuse his own uncoordinated assaults by exaggerating the amount of time it took Burnside to make his attack.) In the meantime, McClellan's refusal to pursue Confederate commander Robert E. Lee aggressively after the battle incensed U.S. president Abraham Lincoln, who replaced his commander with Burnside. His attack on Fredericksburg in December was suitably aggressive, but it was also a disastrous loss for Union forces that involved repeated frontal assaults on heavily fortified Confederate lines. By the end of the battle, Burnside was intensely frustrated and offered to personally lead a final charge before being dissuaded by his subordinates. The engagement's failure was due in part to misunderstandings with Major General William B. Franklin, who had commanded the Union left; subversion by Franklin's generals led to Burnside's removal early in 1863. But this came only after a disastrous, rain-soaked retreat known as the "Mud March," during which nearby Confederate pickets held up signs that mockingly read, "This Way to Richmond."

As commander of the Department of the Ohio in May 1863, Burnside attempted to impose military discipline on the civilian population by arresting Ohio's outspoken antiwar politician, Clement L. Vallandigham, on charges of sympathizing with the enemy. Vallandigham's conviction by military tribunal marked a low point both in Burnside's career and in the Lincoln administration, which supported the arrest and the attendant suspension of habeas corpus. (Vallandigham, a Democrat, would be nominated for Ohio governor in 1864 while in exile in North Carolina.) That summer of 1863 Burnside liberated East Tennessee from Confederate control, but after the Union defeat at the Battle of Chickamauga, Major General William Rosecrans unfairly blamed Burnside for not coming to his aid, although he could only have done so by abandoning East Tennessee.

Burnside returned to Virginia and led the Ninth Corps through the Overland Campaign and into the siege of Petersburg in the spring of 1864. After the entrenched Union and Confederate forces fought to a stalemate outside the city, Burnside encouraged the remarkable idea of excavating a 511-foot-long mine that would end twenty to thirty feet beneath a Confederate artillery battery at Colquitt's Salient. After nearly a month of digging, the mine was packed with explosives and detonated, after which the Ninth Corps assaulted the Confederate lines. Incompetent generals in the leading division compromised the attack, however, and when Union general-in-chief Ulysses S. Grant called off the operation, Burnside's men became trapped in the explosion's crater, serving as easy targets for what a Confederate general later described as a "turkey shoot." Afterward, Grant issued Burnside a leave of absence and never called him back to duty.

Although Burnside has been lampooned as a particularly poor general, that reputation is not fully deserved. He tended to give his subordinates too much latitude, a policy that succeeded so long as those subordinates were experienced professionals, but the amateurs who rose to the top through battlefield attrition required a tighter rein than he was accustomed to administering. The worst charges against him, however, have been filed by those who found him to be a convenient scapegoat for themselves or their allies.

Following the war, Burnside was three times elected governor of Rhode Island and was twice elected to the U.S. Senate. He was president of the Grand Army of the Republic, a Union veterans association, and, in 1871, became the first president of the National Rifle Association. He died on September 13, 1881, in Bristol, Rhode Island.