Upon arrival, Bartlett lived with Rev. Joseph Seccombe. Living with Seccombe, Bartlett had the opportunity to explore a vast and valuable library where he was able to improve in medicine. Bartlett's expertise and concern for his patients led to him becoming a popular and prosperous doctor. In 1752, Bartlett experienced a life threatening fever and treated himself. Years later, he treated patients for diphtheria, which killed 114 people in Kingston. He successfully treated his patients (including his own children), with a new procedure: Peruvian bark (quinine). His success in combating this plague, earned him respect.
Growing in popularity, Bartlett was elected town selectman in 1757. In 1765, he was chosen to represent Kingston in the New Hampshire Provincial Assembly. By 1774, Bartlett had become an active patriot and firm supporter of colonial interests. Bartlett became head of the then illegal Committee of Correspondence of the Provincial Assembly. Here, he was in communication with Samuel Adams and other patriots. Bartlett was chosen to be the representative of New Hampshire in the First Continental Congress, but he was unable to accept because his home had been burnt down by loyalists who opposed his patriotic endeavors. He immediately rebuilt his home on the same site and it stands there to this day.
On July 2, 1776, when voting for independence, it was said that He made the rafters shake with the loudness of his approval. On July 4, he was the first to vote in favor of adopting the Declaration of Independence and a month later, he was the second person to sign it.