Nathan George Shelley was born on February 20, 1826, in Hawkins County, Tennessee, to William Parke Shelley and Margaret Etter. The family moved to Alabama when he was a child, and his father worked as a brick mason. Shelley attended Emory and Henry College in 1841, but financial troubles forced him to withdraw and return home to Alabama. When the Mexican American War broke out, Shelley enlisted in Company E of the First Alabama Infantry, which was commanded by his uncle. After the war, he worked as a clerk in a grocery business before being admitted to the Alabama bar in 1849. He edited the Alabama Reporter and won a seat in the Alabama legislature in 1851. He married Sarah F. Shelley in 1853, and they had at least six children. The family moved to Austin, Texas, in September 1855, and worked as a lawyer there. In 1861, he was elected to the Texas senate as a Democrat.
During the Civil War, Shelley served as a brigadier general with Texas’s state troops. He also became the state’s attorney general in February 1862, and he briefly served in the Confederate army. After the war, he signed an oath of amnesty in November 1865 and resumed his legal practice. He was re-elected to the state senate in 1866 and 1872, and he died in Austin on January 5, 1898.