James W. McMullen was born around 1841 in Indiana to John McMullen and Clarissa Watkins. His father died soon afterward, and his mother married Nathan Smith on July 25, 1844. McMullen married Julia Ann Hubbard on October 3, 1861, and they had at least three children: Ella, born around 1866; Lillie, born around 1870; and John, born around 1873.
He enlisted in the Union army on September 13, 1862, and he mustered in as a private in the 10th Indiana Light Artillery Battery later that day. The regiment took part in the Battle of Perryville, the Battle of Stones River, the Battle of Chickamauga, the siege of Chattanooga, the Battle of Lookout Mountain, and the Battle of Missionary Ridge. He mustered out on July 10, 1865. They settled in Darlington, Indiana, after the war, and McMullen worked as a butcher. They moved to Frankfort, Indiana, in the late 1800s, and by 1900, McMullen was working as a school janitor. He died there on January 11, 1910.