Born in New Orleans, Clark moved to Texas in 1842 and set up a law practice. Clark 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 under 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, but returned home to Marshall, Texas, where he died. His grave in the Marshall City Cemetery is marked with a historical marker.
Clark was an honors graduate of Dartmouth College and received a law degree from Harvard Law School.
During the campaign, Clark positioned himself as a peace candidate and tailored his appeal to liberals and progressives unhappy with the resumption of Selective Service registration and the arms race with the Soviet Union.
Ed Clark's running mate in 1980 was David H. Koch of Koch Industries, who pledged part of his personal fortune to the campaign in exchange for the Vice Presidential nomination.