He was one of ten children of John Shackelford (1736–1800), a soldier in the American Revolutionary War, and Frances Wade Butler (1736-unknown).
However, his proper rank of lieutenant is reflected in a letter to sisters Ann and Frances, and it is believed the assignation of general is revisionist based upon his later career in the area's Indian conflicts.
Shackelford served under General Andrew Jackson, later 7th President of the United States, at the Battle of New Orleans in January 1815.
During the 1836 Indian Wars along the Chattahoochee River, he worked with Generals Winfield Scott and Thomas Jesup.
In 1845, the year Andrew Jackson died, Shackelford wrote to him as a result of the continuing political controversies surrounding General Winfield Scott's removal from command.