 In 1844 and 1846, Chapman was elected as a Whig to the Twenty-ninth and Thirtieth Congresses, serving from March 4, 1845 to March 3, 1849.During the Thirtieth Congress, he served as chairman of the Committee on the District of Columbia.After his tenure in Congress, Chapman resumed the practice of law at Port Tobacco, and served as president of the State constitutional convention in 1851.