Thomas was born in Pelham, Massachussets, on June 11, 1762. He was probably descended from John Thomas who came to Massachusetts from London about 1635 and settled at Marshfield. He was the son of David Thomas and Elizabeth (Harper), his second wife.
After participation in 1777 in expeditions of Massachusetts troops for the relief of Rhode Island, the boy was apprenticed to a shoemaker in Worcester, but in 1781 reëntered the army, serving with the 3rd and 5th Massachusetts regiments and ultimately reaching the rank of sergeant.
Shortly after the war he went to Salem, N. Y. , where his father's sister had her home. Here, in 1784, he married. For some years he kept a tavern in partnership with his brother-in-law. In 1793 he was elected to the Assembly and immediately evinced Republican orthodoxy by moving for the election of the Assembly from single-member districts, a principle embodied fifty-two years later in the constitution of 1846.
He was again elected to the Assembly in 1798 and in 1799. Meanwhile, he was active in the state militia and in 1805 attained the rank of major-general, in command of the 3rd Division. In 1800 he was elected to Congress from the seventh New York district. He served four terms, maintaining fairly consistent regularity as a supporter of the Jefferson administration. On March 29, 1806, he moved a resolution for an amendment to the federal Constitution providing for the choice of presidential electors by districts within the states.
On February 17, 1808, he resigned his seat to accept the office of treasurer of the state of New York. This position he held until February 10, 1810, when Federalist control of the legislature turned him out, but he was elected to the same position by a new legislature in 1812. He achieved a wide acquaintance among the figures in New York's political life and developed a reputation for great sagacity in political diagnosis and manipulation. He also became prominently identified with the cause of DeWitt Clinton. Under these circumstances, his acceptance in 1811 of the position of agent for the Bank of America in its application for a charter exposed him to savage attack. During the summer of that year he traveled over the state in the campaign to get legislators committed to the cause of the Bank before the beginning of the session of 1812. He was subsequently indicted for attempted bribery of a state senator, and was tried, September 17-18, 1812. The trial aroused intense popular interest, since the affair was regarded as a political prosecution. Though he was acquitted, his canvass for reëlection to the treasurership in February 1813 resulted in defeat. This experience seems to have led to his determination, in the prime of life, to retire not only from politics but also from residence in the state.
In 1784, he married Jeannette Turner, his aunt's daughter. His first wife had died in 1795, leaving one daughter, and on January 15, 1800, he had married Mary Hogeboom of Claverack, N. Y. They separated, Thomas arranging for her to live with her sister in Troy, N. Y. , while he went to his sister in Providence, R. I.
