He was the little known older brother to old west lawman Virgil Earp and lawman/gambler Wyatt Earp.

James Earp was born in Hartford, Kentucky and was raised in a tight-knit family environment. In 1861, at 19, he enlisted in the Union Army at the outbreak of the American Civil War, joining the 17th Illinois Infantry. His brothers Virgil and Newton Earp also enlisted. His service was cut short when he was badly wounded in a battle near Fredericktown, Missouri, on October 31, 1861. Newton and Virgil served until the end of the war.

Following the war, James moved around quite frequently, which was an Earp family trait. He lived in Colton, California, Helena, Montana, Pineswell, Missouri and Newton, Kansas, before marrying former prostitute Nellie Ketchum in April 1873. For a while after that he worked in a saloon in Wichita, Kansas, then he worked as a deputy sheriff in Dodge City, Kansas, under Sheriff Charlie Bassett.

In 1879, he moved with his wife to Tombstone, Arizona, where his brothers Wyatt, Virgil were settling. Brother Morgan and his wife Louisa would join them there sometime in late 1880. The three younger brothers became involved in law enforcement in Tombstone, while James opted to work as a manager in a saloon and in gambling houses. Thus, he was not actively involved in the famous Gunfight at the OK Corral in 1881.

Following the murder of his brother Morgan in a pool hall on March 18, 1882, and the ambush and attempted murder of his brother Virgil Earp a couple of months earlier, James left Tombstone serving as an armed escort for his brother Virgil and the rest of the family, as they relocated to Colton, California. Wyatt Earp and James' youngest brother Warren Earp—along with gambler Doc Holliday, gunmen Sherman McMasters, Turkey Creek Jack Johnson and Texas Jack Vermillion—then hunted down those they held responsible for the attacks, in what would be dubbed the Earp Vendetta Ride.

James and Virgil Earp returned brother Morgan's body home to Colton, California, where Morgan was buried. James then lived for a short time in Shoshone County, Idaho, until settling permanently in California by 1890. He died of natural causes on January 25, 1926, in California.