Mohn emigrated from Norway and later came to Northfield where he became principal of St. Olaf's School. Once Old Main was dedicated in 1878, founder B. J. Muus elected Mohn with duty of maintaining the legacy of St. Olaf College.
Not only did Mohn transition from his role of being principal at St. Olaf's School to becoming president of St. Olaf College, but he also served as secretary for the Board of Trustees, pastor at St. John's Lutheran Church and professor, all at he same time. Mohn proved to be the vital agent in the prosperity of St. Olaf during challenging early years and though its 25th anniversary.