History: Wild West By Timothy H. O'Sullivan

O'Sullivan was born in Ireland and came to New York City two years later with his parents. As a teenager, he was employed by Mathew Brady. When the Civil War began in early 1861, he was commissioned a first lieutenant in the Union Army (Joel Snyder, O'Sullivan's biographer could find no proof of this claim in Army records) and, over the next year, was present at Beaufort, Port Royal, Fort Walker, and Fort Pulaski. There is no record of him fighting. He most likely did civilian's work for the army such as surveying, and he took photographs in his spare time.
After being honorably discharged, he rejoined Brady's team. In July 1862, O'Sullivan followed the campaign of Maj. Gen. John Pope's Northern Virginia Campaign. By joining Alexander Gardner's studio, he had his forty-four photographs published in the first Civil War photographs collection, Gardner's Photographic Sketch Book of the War. In July 1863, he created his most famous photograph, "The Harvest of Death," depicting dead soldiers from the Battle of Gettysburg. He took many other photographs documenting the battle, including "Dead Confederate sharpshooter at foot of Little Round Top", "Field where General Reynolds fell", "View in wheatfield opposite our extreme left", "Confederate dead gathered for burial at the southwestern edge of the Rose woods", "Bodies of Federal soldiers near the McPherson woods", "Slaughter pen", and others.
In 1864, following Gen. Ulysses S. Grant's trail, he photographed the Siege of Petersburg before briefly heading to North Carolina to document the siege of Fort Fisher. That brought him to the Appomattox Court House, the site of Robert E. Lee's surrender in April 1865.