Thomas Leonidas Crittenden was a Union general during the American Civil War.

Crittenden was born on May 15, 1819 in Russellville, Kentucky. He was the son of Senator John J. Crittenden, brother of Confederate general George B. Crittenden and cousin of Union general Thomas Turpin Crittenden .

Crittenden was admitted to the bar and served in the US army during Mexican-American War as an aide to General Zachary Taylor and as colonel of the 3rd Kentucky Volunteer Infantry. After the war's end he served as US consul in Liverpool.

When the Civil War began in 1861 he and his father remained loyal to the Union but his brother joined the Confederate army. He was appointed brigadier general of volunteers in September and placed in command of the 5th Division in the Army of the Ohio. He led the division at the Battle of Shiloh in 1862. After Shiloh he was appointed major general of volunteers and commanded the II Corps in the Army of the Ohio during the Confederate Heartland Offensive althoug his corps was only lightly engaged in the fighting. When William S. Rosecrans assumed command of the army, Crittenden's forces were redesignated the Left Wing of the Army of the Cumberland and was heavily engaged at the Battle of Stones River. The Army of the Cumberland was reorganized and Crittenden's corps was once again renamed, this time the XXI Corps. He led the corps through the Tullahoma Campaign and at the Battle of Chickamauga. Crittenden and fellow corps commander Alexander McDowell McCook were blamed for the defeat and relieved of command but both were later exonerated and acquitted of any charges. In 1864 he assumed command of the 1st Division, IX Corps and led it during the Battle of Spotsylvania and the Battle of Cold Harbor before resigning in December, 1864.

After the war he served as the state treasurer of Kentucky and was appointed to the regular army before retiring in 1881. He died in Staten Island, New York on October 23, 1893.