Harold Thorp Carswell was born in Boston, MA, and was educated in private schools in that city. Following graduation, he took classes at the School of Mechanic Arts in Boston and entered the firm of Cram & Ferguson
. His first experience in the Philadelphia area came in 1917 when he was sent by the firm as consulting architect for the Bryn Athyn Cathedral. As that project came to a close, he continued to serve as consultant to businessman Raymond Pitcairn on the continuation of the construction. Altogether he spent some ten years in the office of Cram, Goodhue & Ferguson/Cram & Ferguson before launching his own practice. His first professional listing in the Philadelphia area occurs in 1924, when he is listed as partner in the firm of Walker & Carswell
, with Englishman John Arthur Walker
, who had also come from Cram & Ferguson to work on Bryn Athyn Cathedral. This association with Walker continued loosely until Walker's death in 1938 although the Walker & Carswell partnership is not listed after 1926. George Lovatt's obituary for Carswell indicates also that after his association with Walker, Carswell worked with Robert Tappan
, yet another alumnus of the Bryn Athyn work. Lovatt states that, with Tappan, he was engaged only in residential work "in and about New York." According to Robert Gorman, Carswell worked for George Lovatt, Sr.
before establishing a firm around 1930 with Dominique Berninger
and John A. Bower
(another Lovatt employee) in Jenkintown, PA.
Carswell joined the AlA in 1926. Throughout his career in the Philadelphia area, he maintained his residence in Bryn Athyn, PA.