Background
He was born as Johann Rudolph Niernsee in Vienna, Austria and immigrated to the United States in 1837, at age 22. He apprenticed to Benjamin Henry Latrobe, II, (1806-1878), engineer and manager at the B. & O. and other railroads, (and son of another well-known architect, his father Benjamin Henry Latrobe, 1764-1820).
Career
He served as the head architect for the Baltimore and Ohio Railroad (B & O). In 1847, with James Crawford Neilson, (1816-1900), he formed the Niernsee & Neilson architectural firm that largely served the Baltimore and Ohio Railroad, (B & O). He is credited with having mentored Ephraim Francis Baldwin, (1837-1916), another well-known Maryland and Baltimore architect (and formed the similarly locally-famous firm Baldwin & Pennington with Josias Pennington, ), who also designed buildings and stations for the Baltimore and Ohio Railroad (B & O).
During the American Civil War Niernsee served in the Confederate States Army as a Major. c. ca.
(Niernsee & Nielson), (Niernsee & Neilson).