Born at Cook Settlement, near Farmington, St. Francois County, Missouri, Arnold attended the common schools. Professor at Arcadia College in 1870 and 1871. Deputy clerk of the circuit, county, and probate courts of St. Francois County, Missouri. He studied law. He was admitted to the bar in 1872 and commenced practice in Commerce, Missouri. He served as prosecuting attorney of Scott County 1873-1876. He served as member of the State house of representatives 1877-1879.
Arnold was elected as a Democrat to the Fifty-second and Fifty-third Congresses (March 4, 1891-March 3, 1895). He was an unsuccessful candidate for reelection in 1894 to the Fifty-fourth Congress. He resumed the practice of law in Benton, Missouri, and died there June 12, 1913. He was interred in Benton Cemetery.
- Marshall Arnold at the Biographical Directory of the United States Congress
- Marshall Arnold at Find-A-Grave