He was born August 8, 1836, at York Springs, and he was the eldest of eight children in the family. He attended Cumberland Valley Institute and Juniata Academy where he excelled in mathematics and civil engineering.
In 1857 he was hired by the United States government as an engineer assigned to survey government lands in Nebraska. He returned to the area in 1859 and settled in Baltimore working for the Adams Express Company. After the firing on Fort Sumter he enlisted in Company K, First Regiment Pennsylvania Reserves.
Enlisting as a private he was almost immediately promoted to sergeant. Several months later he was promoted to lieutenant of Company K and then regimental adjutant. The regiment marched to Dranesville and then to Manassas and it ended up camped at Falmouth, Virginia. The First then reported to assist General McClellan's forces and started in on the Peninsula Campaign.
At the Battle of Glendale, the adjutant was wounded by a minie ball that hit the left thigh. To add insult to injury, he was captured by the Rebels and sent to Libby Prison, in Richmond, Virginia Unbeknownst to him, he was promoted to captain on June 30, 1862.
His stay in prison was short and he was exchanged in September. He was sent to David's Island General Hospital located in New York State, to convalesce. He was able to rejoin the 1st PA Reserves at Sharpsburg, Maryland, just after the Battle of Antietam.
The First was at the Battle of Fredericksburg and participated in General Ambrose Burnside's Mud March. It missed Chancellorsville since it was assigned to the Defenses of Washington but it was back in the field in late June to join in on the Gettysburg Campaign. By this time our accomplished and intrepid soldier attained the rank of lieutenant colonel, surely a rising star.
At the Battle of Gettysburg the First was sent to stabilize the Union line in the Wheatfield area and indeed it did. As night fell on July 2, the regiment held its position behind a stone wall at the northern end of Houck's Ridge. On July 3 the regiment assisted in regaining some ground in the Wheatfield. During this battle the young lieutenant colonel was in charge of the operations of the skirmishers.
The PA Reserves continued with the Army of the Potomac for the remainder of 1863 and in 1864 participated in Grant's Overland Campaign. The First left the front June 1, 1864, because the three year enlistments expired however some of the soldiers did reenlist for other service. The indefatigable lieutenant colonel eventually became colonel of the 192nd Pennsylvania Infantry. Finally our soldier mustered out of service on August 24, 1865.
His promotion to colonel was a brevet promotion for gallant conduct at the Battles of the Wilderness and Spotsylvania Court House. On March 13, 1865, he received a brevet promotion of brigadier general for gallant conduct at the Battle of North Anna River.
After the war, General William Warren Stewart worked as a civil engineer for several railroads and for the federal government. His remarkable service in the army and his career as an engineer reflect his natural ability as an intellectual and leader of men.
He died in Chambersburg on March 18, 1916, and is buried in the Presbyterian Graveyard in York Springs.