Jackson was born in Paris, Tennessee. He moved to Jackson, Tennessee with his parents at the age of eight. He graduated from West Tennessee College in 1849, the University of Virginia in 1854, and the Cumberland School of Law in 1856. Upon admission to the bar, he practiced in Jackson and later (1859), Memphis. During the Civil War, he served the Confederacy as a Receiver of Sequestered Property (the vast majority of which was seized from Union sympathizers).

After his civil rights were restored, he returned to Jackson in 1874 and served on the Court of Arbitration for West Tennessee on two occasions. He was elected to the Tennessee House of Representatives in 1880 and from that body elected by the Tennessee General Assembly to the United States Senate, serving from March 4, 1881 until April 14, 1886, when he resigned to accept appointement by President Grover Cleveland to the United States Court of Appeals for the Sixth Circuit. He served on that court until 1893, when Benjamin Harrison, despite the difference in their respective political parties, nominated him to Associate Justice of the Supreme Court of the United States upon the death of Lucius Q. C. Lamar. Howell served on the Court until his death. He is buried in Nashville's Mt. Olivet Cemetery.