Born in Cornwall Hollow, Connecticut on Sept 13, 1813, Sedgwick attended Sharon Academy briefly and taught school for 2 winters before entering West Point where he graduated 24th in the class of 1837. Affectionately called "Uncle John" Sedgwick by his troops, he became the third and final corps commander in the Army of the Potomac to be killed in action.

This Connecticut-born West Pointer had an unusually active prewar career. Originally posted to the artillery, he fought in the Seminole War, was involved in the Trail of Tears episode, and earned two brevets in the Mexican War. Upon the expansion of the regular establishment in 1855 he transferred to the mounted arm. In this branch he served in "Bleeding Kansas," on the Mormon Expedition, and in further Indian fighting. During the secession crisis he was twice in a matter of weeks promoted to replace Robert E. Lee, once when that officer was himself promoted and once when Lee resigned.

Sedgwick's Civil War assignments included: major, 1st Cavalry (since March 3, 1855); lieutenant colonel, 2nd Cavalry (March 16, 1861); colonel, 1st Cavalry (April 25, 1861); colonel, 4th Cavalry (change of designation August 3, 1861); brigadier general, USV (August 31, 1861); commanding 2nd Brigade, Heintzelman's Division, Army of the Potomac (October 31 1861-February 9, 1862); commanding Stone's (old) Division, Army of the Potomac (February 9-March 13, 1862); commanding 2nd Division, 2nd Corps, Army of the Potomac (March 13-September 17, 1862); major general, USV July 4, 1862); commanding 2nd Corps, Army of the Potomac (December 26, 1862-January 26, 1863); commanding 9th Corps, Army of the Potomac January 16 - February 5, 1863); and commanding 6th Corps, Army of the Potomac (February 4 1863-April 6, 1864 and April 13-May 9, 1865).

Initially in charge of a brigade in the fall of 1861, Sedgwick took over a division when General Charles P. Scone was placed under arrest. This he led to the Peninsula where he fought at Yorktown and Seven Pines. During the Seven Days he was wounded at Frayser's Farm. On the nation's birthday he received the second star of a major general and continued in division command until Antietam where his division marched into a trap, being struck on three sides. Sedgwick himself suffered three wounds and was out of action until after Fredericksburg when he returned to lead first the 2nd Corps, then the 9th, and finally the 6th. In the Chancellorsville Campaign he commanded Hooker's force at Fredericksburg. He broke through Marye's Heights in an effort to relieve the pressure on his chief but was stopped at Salem Church and was forced to withdraw north of the river. At Gettysburg his corps was in reserve, but he scored a signal success at Rappahannock Bridge that fall.

One of the top corps commanders with the army, he retained command when the five corps were reduced to three. He led his men into the tangled fighting of the Wilderness and then on to Spotsylvania. While placing his corps artillery he was shot by a Confederate sharpshooter in the head. Ironically he had just declared that they couldn't fire accurately at that distance. He died almost immediately. Sedgwick was buried where he was born, in Cornwall Hollow, Connecticut.