during the mexican–american war (1848-1849), colquitt served as a paymaster in the united states army at the rank of major. after the war, colquitt was elected as a member of the united states house of representatives, serving one term from 1853 to 1855. he next was elected to and served in the georgia state legislature. colquitt was a delegate to "the georgia secession convention of 1861": he voted in favor of secession and signed georgia's ordinance of secession on january 19, 1861.