Alexander Keith Marshall (February 11, 1808 – April 28, 1884) was a United States Representative from Kentucky. He was born at Buck Pond, near Versailles, Kentucky. He completed preparatory studies and settled in Nicholasville, Kentucky. Studying medicine, he graduated from the medical department of the University of Pennsylvania in Philadelphia in 1844 and then engaged in the practice of medicine at Nicholasville, Kentucky.
Marshall was a member of the Kentucky constitutional convention held in Frankfort, Kentucky in 1849. He was elected as a candidate of the American Party to the Thirty-fourth Congress (March 4, 1855 – March 3, 1857). After leaving Congress, he moved to Missouri, but returned to Kentucky and settled in Fayette County where he engaged in agricultural pursuits. He died near East Hickman, Kentucky in 1884 and was interred at Lexington Cemetery.