After he resumed the practice of law in Fayetteville, Arkansas, Dinsmore was elected as a Democrat to the Fifty-third and to the five succeeding Congresses. He served from March 4, 1893 to March 3, 1905. He was an unsuccessful candidate for renomination in 1904 to the Fifty-ninth Congress. He resumed the practice of law in Fayetteville, Arkansas, and in later years devoted most of his time to the management of his farming interests. He served as member of the board of trustees of the University of Arkansas.