He was elected as a Republican to the Sixty-fifth Congress to fill the vacancy caused by the death of Ebenezer J. Hill. Merritt was reelected to the Sixty-sixth and to the five succeeding Congresses and served from November 6, 1917, to March 3, 1931. He was an unsuccessful candidate for reelection in 1930, but was again elected to the Seventy-third and Seventy-fourth Congresses, serving from March 4, 1933 until January 3, 1937. During his time in the House, he served alongside Rep. Matthew Merritt, of New York, who shared a last name, causing some papers to misreport their votes on certain bills. In 1936, Merritt again ran for reelection to the Seventy-fifth Congress, but was not elected, losing to Alfred N. Phillips.