Born in Missouri on January 15, 1848. He was the ninth of fourteen children born to Henry Washington Younger and Bersheba Leighton Fristoe. Jim Younger joined the Confederate Army during the American Civil War with his brother Cole, eventually joining Quantrill's Raiders in 1864. Jim was later captured by Union troops in the same ambush that resulted in William Quantrill's death. Jim was imprisoned until the end of the war.
After the war Jim tried his hand at various activities, including starting a horse ranch. In 1873 he joined the James-Younger gang, a gang founded by his brother Cole along with Frank and Jesse James.
It's uncertain how much time he spent with the gang, but he was present when his brother John was killed by Pinkertons in Roscoe, Missouri in 1874. He left the gang and spent the next two years working a ranch in San Luis Obispo, California.
Jim returned to the gang in time to join the ill-fated 1876 bank job in Northfield, Minnesota. Part of his jaw was shot off and he was captured and sentenced to life imprisonment. He was paroled in 1901 with his brother Cole. After his release he became engaged to Alix Mueller, who had met him in prison 20 years after the Northfield robbery. Due to the terms of his parole however Jim couldn't marry, so he committed suicide on October 19, 1902. His body was returned to Lee's Summit, Missouri for burial.