Early in 1861, because of the impending Civil War, Major Sedgwick was ordered to report to the War Department in Washington, D.C., where on March 16, 1861, he was appointed Lieutenant Colonel of the Second Cavalry and on April 25, Colonel of the First Cavalry and again on August 3, Colonel of the Fourth Cavalry. On August 31, he was made Brigadier General of U.S. Volunteers and July 4, 1862, Major General U.S. Volunteers.

Major General Sedgwick saw continuous service in the Army of the Potomac, except for about three weeks when he was allowed to go home to recuperate from three wounds received at the battle of Antietam, until his death May 9, 1864. He was in command of several different Army Corps but principally the Sixth and Second. He has been credited by some authorities with turning the tide of battle by his prompt arrival at Gettysburg after a forced march of 35 miles during the night.

General Sedgwick declined the command of the Army of the Potomac just before it was given to General Meade but several times held it temporarily during that General's absence. He was very fond of horses and owned several exceptionally fine. While in command of the Second Army Corps, the men and officers of his division presented him with a horse reputedly the finest in the Army. The horse and its equipment cost seventeen hundred dollars. The sword accompanying it was orderd from France and cost a thousand dollars. The gift indicated the affection and esteem felt by those under his command.

Several monuments have been erected to the memory of Major General Sedgwick. One at the West Point Military Academy was dedicated October 21, 1868, when the orator of the day said in