Alexander T. Hawthorn was born on 10 January 1825 near Evergreen, Conecuh County, Alabama. He attended Evergreen Academy and Mercer University. He studied law at Yale University in 1846 and 1847. After leaving Yale he relocated to Camden, Ouachita County, Arkansas and opened a law practice.
At the outbreak of the Civil War Hawthorn organized the 6th Arkansas Infantry Regiment and was elected Lieutenant Colonel. By 1862 he had advanced to Colonel of the regiment. Hawthorn led the 6th during the Battle of Shiloh.
Hawthorn was not reelected after 6th Arkansas was reorganized and he was reassigned to the Trans-Mississippi Department and returned to Arkansas.
On 28 February 1864 Hawthorn received his commission as Brigadier General. Hawthorn participated in the Arkansas portion of the Red River Campaign and commanded his brigade at the Battle of Jenkins' Ferry under General Thomas James Churchill.
After the war Hawthorn emigrated to Brazil but moved to Atlanta, Georgia in 1874 and established a career in business. In 1880 Hawthorn was ordained into the Baptist ministry and thereafter moved to Dallas, Texas.
Hawthorn died in Dallas, Texas on 31 May 1899 and is buried at Greenwood Cemetery in Marshall, Harrison County, Texas.