Born in Fairhaven, Ohio, Caldwell was educated in the common schools of his native county and also by private teachers.
He taught school for several years.
He was graduated from the Cincinnati Law School in 1876.
He was admitted to the bar the same year.
He again engaged in teaching.
He commenced the practice of law in Cincinnati, Ohio, in 1878.
He served as prosecuting attorney of the Cincinnati police court 1881–1885.
Caldwell was elected judge of the city police court in 1887.
Caldwell was elected president of the Ohio League of Republican Clubs in 1887.
Caldwell was elected as a Republican to the Fifty-first, Fifty-second, and Fifty-third Congresses and served from March 4, 1889, until May 4, 1894, when he resigned.
He served as mayor of Cincinnati from 1894 to 1897 and as the lieutenant governor of Ohio from 1900 to 1902.