Thomas Carstairs was an "Architect and House-carpenter" from Largo, County Fife, Scotland, first noted in Philadelphia when he announced in the Pennsylvania Packet
(February 5, 1784) that he had "lately arrived in this city from London, [and] begs leave to inform the Public, that he intends to follow his profession in all its various branches. Being regularly bred to it, and well acquainted with all its modern improvements, he flatters himself he will give satisfaction to such gentlemen as please to employ him." That same year -- in what must have been viewed as a considerable breach of etiquette -- he petitioned The Carpenters' Company for membership, but he was not elected until 1788; he then ignored the invitation. In 1789 he received the second prize of five pounds in the Library Hall competition won by William Thornton
The only commission that can firmly be attributed to Carstairs is a block of twenty-two speculative row houses designed for William Sansom and erected on the south side of the newly developed Sansom Street between Seventh and Eighth Streets, c.1800-1802, for which a single sheet plan and elevation is preserved at the Library Company of Philadelphia.
Carstairs, together with William Williams, may be an important link to British neo-classicism in Philadelphia. How quickly Carstairs established himself in Philadelphia is shown in 1793 when Stephen Hallet and James Hoban attacked William Thornton's design for the United States Capitol. President Washington, at his wits' end over the bickering between these three, sent Hallet and Hoban to Philadelphia to meet with Samuel Blodget, Superintendent of Public Buildings, and Thornton. Since Blodget also thought Thornton's plan "impraticable," Thornton arrived at the meeting with William Williams and Thomas Carstairs as his advisors. The amateur architect, Secretary of State Thomas Jefferson presided over this extraordinary meeting that resulted in some changes in the Thornton plan.
According to the Historical Catalogue of the St. Andrew's Society, Carstairs was born in Largo, Fifeshire, Scotland, to Daivd and Margaret (Fair) Carstairs. He was baptized in the parish church of Largo on 23 August 1759 and came to Philadelphia in 1780. Carstairs is listed in the Philadelphia city directories as a house carpenter, 1796-1807, and as a house carpenter and "draughtsman" at 76 S. Eighth Street from 1809 to 1819. In 1804 he was reelected to The Carpenters' Company and this time signed the articles on January 21, 1805.