Stallo was born in Sierhausen in the Grand Duchy of Oldenburg (Germany) on March 16, 1823, the son of a schoolmaster, Johann Heinrich Stallo (1797-1840) and his wife, Anna Maria Adelheid Moormann (1798-1861).
Stallo taught German and Mathematics at the newly renamed St. Xavier College (formerly a Jesuit "lyceum" called "The Atheneum") from 1841-1844.