Civil War Union Brigadier General. Born in Scotland, he learned the blacksmithing trade before immigrating to the United States in 1849. Settling in Chicago, Illinois, he worked first as a boilermaker before founding the Excelsior Iron Works with his brother-in-law, serving as it's proprietor. When the Civil War broke out in April of 1861, he helped recruit an infantry regiment that drew it's ranks largely from Chicago's Scottish community. When the regiment was mustered into Federal service as the 12th Illinois Volunteer Infantry, John McArthur was appointed it's Colonel and commander on August 1, 1861. He led his unit until January 1862, when he was advanced to brigade command. His abilities were tested in the February 1862 Battle of Fort Donaldson, where his out-positioned brigade suffered heavily in the face of a Confederate breakout attempt, but retired in an orderly manner. Promoted to Brigadier General, US Volunteers on March 21, 1862, he was in command of the Union Army of the Tennessee's 2nd Brigade of the 2nd Division at the April 1862 Battle of Shiloh, where he was wounded. He returned from his wounds to the field in time to lead his troops at the May 1862 First Battle of Corinth. Advanced to Division command and sent to the Army of the Mississippi under Major General William S. Rosecrans, a mistake in orders found him temporarily without a command during the October 1862 2nd Battle of Corinth. When the mistake was discovered, he was assigned to command a brigade during the battle. Eventually returned to command of the VI Division, XVII Corps, Army of the Tennessee, he would lead it through the balance of the war, fighting with his men in the Spring-Summer 1863 Vicksburg Campaign, in the December 1864 Battle of Nashville, and in the April 1865 capture of Fort Blakely, Alabama. Brevetted Major General, US Volunteers to date from December 15, 1864 for his service in the Battle of Nashville, he was honorably mustered out of service on August 24, 1865. After returning to civilian life, General McArthur struggled with career challenges. His iron business did not succeed, and his position as Chicago public works commissioner ended after the October 1871 Great Chicago Fire. He served as Postmaster of Chicago, but was found culpable for losing $73,000 of postal funds in a bank failure. He died in Chicago, Illinois in 1906.