Civil War Union Brigadier General. He enlisted in the 27th New York Volunteer Infantry in May 1861 after the outbreak of the Civil War, serving as Major of the regiment, whose first Colonel was Henry W. Slocum. In this capacity he fought with his regiment at the 1st Battle of Bull Run. When Colonel Slocum was promoted to Brigadier General in September of that year, Joseph Bartlett was advanced to Colonel and commander of the unit. He had led the 27th New York in the open actions of the Spring 1862 Peninsular Campaign, but assumed command of the 2nd Brigade, 1st Division of the Army of the Potomac’s VI Corps on May 18,1862. He commanded the brigade in the subsequent Battles of the Seven Days, 2nd Bull Run (where it was not engaged), South Mountain (where it fought heavily at Crampton’s Gap) and Antietam (where it was lightly engaged in the East Woods area). In October 1862 he was promoted to Brigadier General, US Volunteers, but his commission was not confirmed by the United States Senate, and it expired by law on March 4, 1863. However, due to the fact that he had been repeatedly commended by superior officers during his service, he was re-appointed Brigadier General on March 30, and his commission was then confirmed. He would alternate between Brigade and Division command though the rest of the War. At the Battle of Gettysburg in July 1863, he led his own brigade as well as that of another in defensive positions north of Little Round Top, and saw no fighting. The day after the Battle he assumed command of the VI Corps' Third Division, and led it through the Summer. In the Fall 1863 Mine Run Campaign, he was almost captured by Major General J.E.B. Stuart’s cavalry forces at New Baltimore, Virginia, having to flee wearing only bed clothing. He would go on to fight in the 1864 Overland Campaign and the Siege of Petersburg. In April 1865, when the Confederate Army of Northern Virginia surrendered at Appomattox Court House, he, in his capacity as the closest division commander, received the stacked arms of the Confederates’ during their surrender. He continued to serve until his muster out in January 1866, having received the brevet of Major General, US Volunteers. After the war he was appointed as United States Minister to Sweden, serving from 1867 to 1869.