He graduated from Harvard in 1786 and applied himself to the practice of medicine in Stockbridge, Massachusetts. Sometime thereafter, he removed to Albany to join a medical supplies business in partnership with druggest Samuel Dexter. As early as November 1787, these transplanted New Englanders were advertizing in the Albany newspaper as apothecaries at 47 Market Street.
In April 1797, he married Eliza Sedgwick - eldest daughter of Theodore Sedgwick of Stockbridge. Ten years older than his young bride, the marriage produced twelve children between 1798 and 1817. His wife belonged to the Albany Presbyterian church.
In 1806, family health concerns moved him to retire to Stockbridge where he became a farmer who bred sheep and was involved in community affairs for the next four decades. He was a trustee of Williams College.
Sources: The life of Thaddeus Pomeroy has not been assigned a CAP biography number. This sketch is derived chiefly from family and community-based resources. Online resources: Pomeroy family;
Local Obituary: "His strongly marked character, in which were blended qualities not always united, exerted a large and salutary influence. To fine physical courage and an energy that never failed, he added a humane and equitable temper. From early training and habit, he was frugal and economical, yet always generous and hospitable, liberal in any public enterprise, and always ready to assist his less prosperous neighbors. In his religious opinions, he adhered to the faith of his orthodox fathers, but his sympathies were not confined to any one creed, and he honored Christianity under whatever name. His truth was unalterable ; his honesty inflexible ; his friendships unchanging ; his enmities strong and his prejudices unyielding. To a social disposition, and a vein of humor peculiarly his own, he added a courtesy of the old school, and until the last days of his life never relaxed in those little attentions to his person which he considered a part of the manner of an American gentleman. Through a long and distressing illness his consciousness remained to the last, and he looked death in the face, not only without fear but with the confidence of a Christian, leaving an example of those hardy virtues, the natural growth of times of conflict and difficulty, without which no person however prosperous can be safe or respectable. With a manner sometimes abrupt, perhaps even harsh, he had a woman's tenderness, with a wholesome regard for order and method, but was inclined to resent a trespass in his respect for principle." óLocal Obituary. source