Born in the Frankford section of Philadelphia in 1868, Horace Trumbauer left school at the age of fourteen and entered the architectural firm of G. W. and W. D. Hewitt as an "errand boy." He was soon promoted to draftsman. Trumbauer's advancement and acquisition of knowledge enabled him to eventually open his own office (310 Chestnut Street) in 1890.
According to Trumbauer-historian Frederick Platt, the architect received $171.75 for his first commission, a house near Narberth, Pennsylvania. Soon afterward, he landed his first major commission, a mansion in Glenside, Pennsylvania, for sugar baron William Welsh Harrison. When Harrison's mansion burned to the ground in 1893, he commissioned Trumbauer to rebuild it. This second home, called Grey Towers (now part of Arcadia University), marked the architect's rise to prominence in the profession. Its castle-like design instilled the estate with a distinct architectural style that was unique to Trumbauer's work.
After Grey Towers, Trumbauer's firm became known for creating elegant homes for America's elite. For several decades, Trumbauer enjoyed what his stepdaughter called "the big money years." In the 1890's, Trumbauer planned large country houses for the wealthy, smaller suburban houses for developments, like Overbrook Farms, and, several buildings for Willow Grove Amusement Park. While working at the amusement park, Trumbauer developed relationships with its proprietors, the Widener and Elkins families, for whom he would complete numerous commissions. Significantly, traction (trolley cars) magnate Peter A. B. Widener, vice president of the Free Library's Board of Trustees, was instrumental in Trumbauer's receipt of the main Free Library commission in 1911.
In the first years of the new century, Trumbauer's firm expanded its scope, designing not only mansions in Philadelphia, New York City, and Newport, Rhode Island, but also apartment houses and other large structures. Trumbauer married Sara Thomson Williams in 1903 and soon erected a home in the Wynnefield section of the City. By 1904, when the prominent Architectural Record published a lengthy account of Trumbauer's works, he had become one of the country's most distinguished architects.
Over the next decades, Trumbauer and his staff received more than 1000 commissions, including offices, schools, hotels, and medical buildings. With collaborators Zantzinger, Borie & Medary, he created the Philadelphia Museum of Art. Among Trumbauer's most important commissions of this period was the Gothic Revival Duke University campus in Durham, North Carolina.
Trumbauer worked exclusively in period styles, reviving the architecture of distant times and places. For this reason, his work lost favor when the popular pendulum swung toward European Modernism. Because of this trend and the Great Depression, Trumbauer's practice dwindled in the 1930s. His staff fell from a high of thirty members down to his longtime associate Julian Abele and a few others. He died on September 18, 1938.