Niehaus began working as a marble and wood carver and then gained entrance to the McMichen School of Design in Cincinnati and later studied at the Royal Academy in Munich, Germany. The effect of the German study was that he retained much of the neo-classic flavor in his art while most other sculptors of his generation were drawn towards beaux-arts realism.
Niehaus returned to America in 1881 and by virtue of being a native Ohioan was commissioned to execute statue of the recently assassinated President Garfield, who was also from Ohio. Following that he created a statue of Ohioan William Allen that was placed in the National Statuary Hall Collection in the United States Capitol in Washington D.C., along with his statue of Garfield. In later years he was to place statues of John J. Ingalls (Kansas, 1905) Henry Clay (Kentucky, 1929), Ephraim McDowell (Kentucky, 1929), Zachariah Chandler (Michigan, 1913), Oliver P. Norton (Indiana, 1900) and George W. Glick (Kansas, 1914) in the Hall, making his eight statues represented there five more than any other artist.
Monuments by Niehaus can be found in many American cities. Several of the works authored by him are equestrian statues. As was the case with other sculptors of his day he also fashioned a fair amount of architectural sculpture.
Bzdak, Meredith Arms, photographs by Douglas Peterson, Public Sculpture in New Jersey: Monuments to Collective identity, Rutgers University Press, New Brunswick, New Jersey, 1999
Connecticut State Capitol Statuary, The League of Women Voters of Connenticut: Education Fund
Hardin Campen, Richard N., Outdoor Sculpture in Ohio: A Comprehensive Overview of Outdoor Sculpture in Ohio, Mid-Nineteenth Century to the Present, West Summit Press, Chagrin Falls, Ohio, 1980
Kvaran, Einar Einarsson, Architectural Sculpture of America, unpublished manuscript
Opitz, Glenn B , Editor, Mantle Fielding’s Dictionary of American Painters, Sculptors & Engravers, Apollo Book, Poughkeepsie NY, 1986