He was born on July 2, 1923, in New York City to William Bell Dinsmoor and Zillah F. Pierce (1886–1960).
Dinsmoor studied at Phillips Exeter Academy and Columbia University, taking time out for active service in the military during World War II in India and China.
[5] Dinsmoor moved to Greece to assist Lucy Taxis Shoe Meritt with her survey of Greek architectural moulding and Carl Blegen on his books on Troy and Pylos.
[6] In the field, Dinsmoor worked with Oscar Broneer and helped publish the finds of the temple of Poseidon in Athens.
[7] Dinsmoor's main research focused on the propylaia to the acropolis in Athens, working to study its construction and establish its configuration during various phases.