Andrew Gillespie Henderson was born on January 4, 1823, in Harrisburg, Pennsylvania, to Joseph Henderson and Elizabeth Morrison. His family moved to Springfield, Illinois, around 1833, and he worked as an apprentice for the State Journal. He eventually became the editor of the Galena Gazette and (after moving to Iowa) the Dubuque Tribune. He married Sarah Ann Barrow on October 6, 1846, and they had at least six children: John, born around 1848; Sarah, born around 1849; Matilda, born around 1852; Alice, born around 1856; James, born around 1861; and Anna, born around 1863. The family settled in Maquoketa, Iowa, around 1855, and he established the Maquoketa Excelsior. By 1860, he owned $5,000 of real estate and $500 of personal property.
Henderson enlisted in the Union army on August 13, 1862, and mustered in as a 1st lieutenant in Company F of the 31st Iowa Infantry on October 13. He was severely wounded on May 22, 1863, during the Siege of Vicksburg, but he eventually recovered and rejoined his regiment. He took part in the Atlanta Campaign, and he resigned on September 22, 1864. He returned to Maquoketa after leaving the army. He applied for a federal pension in May 1865 and secured one soon afterward. By 1870, he owned $10,000 of real estate and $4,000 of personal property. Sarah died on April 21, 1879. Henderson moved to Sioux City, Iowa, sometime before 1899 and eventually settled in Spokane, Washington. He died in Spokane on February 16, 1899.