Hunter graduated from West Point in 1822, ranked 24 out of 40 in his class. He was assigned to the infantry-Dragoons, where he served on the frontier. After resigning in 1836, he returned to duty during the Mexican War as a major Paymaster. He served in minor positions on the Northwest frontier before the war.
When the Civil War started, Hunter was appointed Brigadier General in May, and put in command of the 2d Division of Brigadier Gen. Irvin McDowell's army. Being promoted to major general in August, he fought at 1st Bull Run and was severely wounded. He was assigned to lead a division in Missouri , where he releived Major Gen. John C. Frémont as commander of the Western Department. He sent detachments to Fort Henry and Fort Donelson and to Brigadier Gen. E.R.S. Canby in New Mexico. Taking over the Department of the South in 1862, he captured Fort Pulaski.
While Hunter abolished slavery in his department on May 9, 1862, President Abraham Lincoln reversed the action, since Hunter had surpassed his authority. He went on to raise the 1st South Carolina, an all-black regiment, which Congress approved. The Confederacy labeled him as a "felon to be executed if captured."
In June 1862, while trying to capture Charleston, South Carolina, Hunter was defeated at Secessionville. After the loss, he was suspended from duty temporarily. He then served on the court-martial of Major Gen. Fitz-John Porter and asked about the defeat at Harpers Ferry. he then served on on a variety of boards and commissions.
In May 1864, Hunter was called to take over the Department of West Virginia after Major Gen. Frank Sigel was defeated in the Shenandoah valley. After cutting Confederate supply, communication and railroad lines, Hunter won a victory at Piedmont. At Lynchburg, he and his troops retreated from Major Gen. Jubal A. Early, leaving the area unprotected and retreating to West Virginia . This left the valley open for Early's Washington Raid. He was criticized for his retreat and, after meeting with Lieutenant Gen. Ulysses S. Grant and Major Gen. Philip H. Sheridan, he resigned his command on August 8, 1864, and served on court-martials from February 1, 1865 until the end of the war. Sheridan was then able to clear the Shenandoah Valley of Confederate troops.
He accompanied Lincoln's body to Springfield, Illinois and returned to Washington, D.C. to preside over the commission that tried the assassination conspirators. He was later brevetted a brigadier and major general in the Regular Army, and lived in Washington, D.C. until his death.
Known for the numerous defeats he suffered, he is not considered among the more adept Union officers.
Colonel - May 14, 1861
Brigadier General USV- May 17, 1861
Major General USV- August 13, 1861
Brigadier General USA- March 13, 1865 (breveted for Piedmont and Shenandoah Valley Campaign)
Major General USA- March 13, 1865 (breveted for war service)
Hunter's Brigade, Army of the Potomac (August 1861)
Department of the South (March 31- August 22, 1862)