Representing New Hampshire at the Continental Congress
Thornton was then selected as the first President of the New Hampshire House of Representatives, and as a justice to the Superior Court, under the new constitution. He was also sent to the Continental Congress-too late to participate in the debates over Independence, but just in time to sign the Declaration on behalf of New Hampshire. This was true, also, of Benjamin Rush, George Clymer, James Wilson, George Ross and George Taylor. But all these gentlemen acceding to the Declaration, were permitted to affix their signatures to the engrossed copy of that instrument.
For the rest of his life, Thornton attended to State duties, practiced medicine and was involved in the agricultural practices of his land holdings. He also wrote political essays for the newspapers. He died at the age of 89, while on a visit to his daughter in Newburyport, Massachusetts, in 1803.