His courage and tactics affected the outcome of some of the most significant battles in the war, including Malvern Hill, Antietam, Fredericksburg, and most notably at Gettysburg, where his operational decisions regarding strategic cannon placement and conservation of ammunition for the Confederate main assault, contributed greatly to the defeat of Pickett's Charge.

He served in the Mexican War under Winfield Scott, and was appointed a brevet captain for gallantry at Contreras and Churubusco and to major at Chapultepec.

Hunt achieved some fame in the First Battle of Bull Run in 1861, when his four-gun battery covered the retreat of a Union force with a close-in artillery duel.

At the Battle of Fredericksburg in December, his gun emplacements on Stafford Heights effectively eliminated any possibility that Gen. Robert E. Lee could counterattack Union forces across the Rappahannock River.

Although acknowledging the power of massed batteries to repel infantry assaults (such as at Malvern Hill or against Pickett's Charge in the Battle of Gettysburg), he urged his gun crews to fire slowly and deliberately and reprimanded them if they exceeded an average of one shot per minute.

A story often told about Hunt was when he exclaimed to a gunner of a fast-firing gun, "Young man, are you aware that every round you fire costs $2.67?"

His new commander, Maj. Gen. George G. Meade, had considerably more respect for Hunt than Hooker did and not only gave him great latitude in directing the artillery, but also used him on occasion as his personal representative.

For example, on July 2, Meade sent Hunt to visit III Corps commander Maj. Gen. Daniel E. Sickles in an attempt to get his defensive lines to conform to orders.

(Sickles' insubordinate movement from Cemetery Ridge, where he had been ordered to defend, to the Peach Orchard caused considerable difficulty for the entire Union defense.)

Hunt was unable to influence the irascible political general, but his masterful analysis of terrain and placement of batteries on the ridge were important factors in the Union's eventual success on the second day.

Later, with the Union line on Cemetery Ridge under massive bombardment from Longstreet's corps artillery chief, Col. Edward Porter Alexander, Hunt was able to resist command pressure from fiery II Corps commander Maj. Gen. Winfield S. Hancock who had demanded Union fire to lift the spirits of the infantrymen pinned down under Alexander's bombardment.

He served as commanding officer of Fort Adams in Newport, Rhode Island, from May 20, 1869, until November 10, 1875, and as president of the permanent Artillery Board.