A native of Ithaca, New York, Grant graduated from the United States Military Academy at West Point in 1900 and began a long career with the Cavalry branch.

He served in the Philippine–American War and China Relief Expedition in the early 1900s, and was a longtime aide-de-camp for several department commanders.

A 1915 graduate of the United States Army Command and General Staff College, Grant performed duty on the Texas-Mexico border during the 1916 Pancho Villa Expedition.

During World War I, he served on the operations staffs of the American Expeditionary Forces headquarters in France, as well as several divisions and corps.

After the First World War, Grant's assignments included command of Fort Adams, Rhode Island and the 13th Cavalry Regiment.

[8] Grant served in leadership roles as cadet corporal, first sergeant and captain until 1900, when he was returned to the ranks after taking part in protests against the academy's attempt to change the treatment of lower classmen by those in the upper classes.

[10] Among his classmates who also attained general officer rank were Upton Birnie Jr., Archibald H. Sunderland and Augustine McIntyre Jr.[11] Grant was assigned to the 6th Cavalry Regiment, and was immediately posted to the Philippines to take part in the Philippine–American War and the China Relief Expedition, which was the U.S. response to the Boxer Rebellion.

[12] After returning to the United States, Grant was assigned to the 3rd Cavalry Regiment, and served as aide-de-camp to Brigadier Generals William August Kobbé and Camillo C. C. Carr, successive commanders of the Department of Dakota.

[12] In 1915, he graduated from the United States Army Command and General Staff College, after which he was detailed to the Signal Corps.

[12] On August 5, he was promoted to temporary major, and lieutenant colonel, after which he was assigned to the operations section (G-3) on the staff of the American Expeditionary Forces in France.

[12] He was promoted to temporary colonel in August 1918, and at the end of the war he was serving as First Army's deputy chief of staff.

The citation read: The President of the United States of America, authorized by Act of Congress, July 9, 1918, takes pleasure in presenting the Army Distinguished Service Medal to Colonel (Cavalry) Walter Schuyler Grant, United States Army, for exceptionally meritorious and distinguished services to the Government of the United States, in a duty of great responsibility during World War I.

As Chief of Staff of the 1st Army Corps, he displayed the same tact, zeal, and energy which marked the previous character of his services.

[12] When the Great Vermont Flood of 1927 took place in early November, Grant helped coordinate federal participation in relief efforts, for which he was commended by the commander of the First Corps Area.

[12] After returning to the United States, he was assigned to command the Third Corps Area, where he served from June 1940 until January 1942, when he reached the mandatory retirement age of 64.

[12] In retirement, Grant was a resident of Washington, D.C.[12] He died at Walter Reed Army Medical Center on March 3, 1956.