Osterling received his training in the office of Joseph Stillburg. Following a period of European travel, he launched his own practice in 1888. During his career he designed many prominent Pittsburgh buildings, such as the Union Trust Building (1915–17). According to Martin Aurand, Architecture Librarian at Carnegie Mellon University in Pittsburgh, Osterling's practice faltered after controversy relating to his anticipated alteration to the landmark H.H. RichardsonAllegheny County Courthouse and a public lawsuit filed by the industrialist Henry Clay Frick. Osterling's studio was in a building he designed himself in 1917 at 228 Isabella Street in Pittsburgh's North Shore neighborhood.
Colonial Trust Company Building, now part of the Bank Center of Point Park University (Wood Street, between Forbes and Fourth Avenues), 1902. Also, Osterling designed a T-shaped lobby that was added to his original building in 1926.
Gwinner-Harter House, also known as the William B. Negley House (5061 Fifth Avenue) was designed by an unknown architect and built 1870-1871. However, Osterling was responsible for additions between 1912 and 1923.
Osterling Flats, date unavailable. These are three houses at 3603-3607 California Avenue with Dutch design elements, which were converted into condos by the Brighton Heights Citizens' Federation in 2003.
The 1889 bell tower from the former Bellefield Presbyterian Church is all that remains in front of the University of Pittsburgh's Bellefield Towers building