At Thomas Jefferson University since 1995, Dr. Breiner teaches theory seminars such as American Architecture and Vernacular Architecture. He has taught all four required History of Architecture and Interiors courses in addition to many electives and 2nd-year architectural studio.  He is also the Associate Dean of the College, tasked with assessment, student development, facilities, and adjunct management, and previously served as Director of the Architecture Program.

His research interests include architecture and urbanism in the United States and Italy and the pedagogy of teaching architectural history. These are reflected in his publications on topics such as the New York firm of Heins & LaFarge, Renaissance architect Vincenzo Scamozzi, and the role of service learning. During his tenure at the Landmarks Preservation Commission in New York City, he wrote designation reports for many significant neighborhoods and buildings, including the Seagram Building and Guggenheim Museum.

Funded by the Getty Trust and Dietrich Foundation, Dr. Breiner undertook a Campus Heritage Project, documenting cultural landscapes on the University's East Falls Campus, which he is expanding into a monograph. Additional funding has facilitated continued research in Italy.

Professor Breiner has served on the boards of the Philadelphia Chapter of the Society of Architectural Historians, the Germantown Historical Society, and the East Falls Historical Society. His other professional memberships include the National Trust for Historic Preservation and the Historical Society of Pennsylvania.