Under the aegis of noted landscape architect Robert Morris Copeland, he relocated to Philadelphia in 1872, to work on development of the planned community of Ridley Park, Pennsylvania.

Chandler married Sophie Madeleine du Pont (1851–1931) of the distinguished Delaware industrialist family on March 8, 1873.

He persuaded Warren P. Laird to move to Philadelphia to succeed him at Penn and develop a curriculum based on that of the École des Beaux-Arts.

He designed alterations to Independence Hall (1878, unbuilt), and doubled the width of John Haviland's 1838 Pennsylvania Fire Insurance Company (1902).

[5] The first retrospective exhibition of his work, Theophilus P. Chandler Jr.: Portrait of an American Architect, was held at the Athenaeum of Philadelphia in 2010.