After his father died in the 1830s, he moved to Montgomery, Alabama with his mother and studied the law.
His term coincided with the beginning of the American Civil War. Clark grew up in Georgia. Clark moved to Texas in 1842 and set up a law practice.
He served in the Texas Annexation Convention and two terms as a state representative in the Texas Legislature before fighting in the Mexican-American War.
When the war ended, he served as secretary of state under Governor Elisha M. Pease and as lieutenant governor serving under Governor Sam Houston. When Sam Houston refused to take an oath of allegiance to the Confederacy, Clark became governor.
After losing the governor"s race by 124 votes to Francis Lubbock, Clark joined the 14th Texas Infantry as a colonel and was later promoted to brigadier general after being wounded in battle. He fled briefly to Mexico at the end of the American Civil War, and returned home to Marshall, Texas.
Clark died on May 4, 1880 in Marshall, Texas.
His grave in the Marshall City Cemetery is marked with a historical mark.