In 1919, Thomas returned to Portland permanently, forming a partnership with architect Charles O. Poor, successor to the practice of Frederick A. Tompson. In 1922, Poor died in a railroad accident, and Thomas continued the business alone. In 1923 he incorporated the firm under his own name, in association with Murray Crosman Binford and Albert Cyprian Hobbs.[4][5] Thomas continued in independent practice for almost twenty years, closing his office in late 1941 upon the United States' entry into World War II. During the war, Thomas, still in the Naval Reserve, was attached to the local Naval Intelligence office.[2][6][3]
During his lifetime, Thomas was known as a talented designer of buildings in revival styles. His works in the Colonial Revival and Gothic Revival styles in particular were intended to invoke the English heritage of both Thomas and Portland.[3] Four of Thomas' works have been listed on the United States National Register of Historic Places, and others contribute to listed historic districts.
The noted Maine architects Royal Boston Jr. and Josiah T. Tubby both worked for Thomas as drafters and designers.[3]
^"John P. Thomas". Maine Memory Network. Retrieved October 18, 2022.
^ abc"John Pickering Thomas" in Maine: Resources, Attractions and People 3, ed. Harrie B. Coe (New York: Lewis Historical Publishing Company, 1928): 40–41.
^ abcdefghijklmnoRoger G. Reed, "John P. Thomas, 1886–1944" in Biographical Dictionary of Architects in Maine 7, ed. Earle G. Shettleworth Jr. (Augusta: Maine Historic Preservation Commission, 1996)
^"New Corporations" in Daily Kennebec Journal, December 24, 1923, 10.