Born on a farm near Downing, Missouri, Arnold attended the Coffey, Missouri, rural schools and was graduated from Kirksville (Missouri) State Teachers College in 1902. He taught school in the Coffey, Missouri, school district in 1896. Superintendent of the public schools in Middletown, Missouri, in 1901 and 1902 and in Atlanta, Missouri, in 1903. He was employed in the St. Louis, Missouri, internal revenue office in 1904. He engaged in the retail lumber business at Atlanta, Missouri from 1905 to 1908. He moved to Kirksville, Missouri, in 1908 and organized the Arnold Lumber Co..
Arnold was elected as a Republican to the Seventy-eighth, Seventy-ninth, and Eightieth Congresses (January 3, 1943-January 3, 1949). He was an unsuccessful candidate for reelection in 1948 to the Eighty-first Congress, for election in 1950 to the Eighty-second Congress, and in 1952 to the Eighty-third Congress. He retired from political and business activities in 1952. He died in Kirksville, Missouri, December 18, 1961. He was interred in Maple Hills Cemetery.