Bartlett was born in Amesbury, Massachusetts and was well educated. At a young age he had a solid foundation in Latin and knew quite a bit of Greek. He studied medicine under Dr. Ordway and before the age of 21 he would move to the frontier town of Kingston, New Hampshire and set up his own practice. When he was 24 he married his cousin Mary Bartlett. The two would have 12 children together. Three of his sons and seven of his grandsons would follow him into the field of medicine.
Bartlett was selected as a delegate from New Hampshire in 1775, and attended that session as well as the meetings in 1776. Most of the work of the Second Continental Congress was carried out in committees. The most important of these required a delegate from each colony/state, which meant that Bartlett served on all of them, including those of Safety, Secrecy, Munitions, Marine and Civil Government.
William Whipple and Matthew Thornton were added to the delegation in Philadelphia after Bartlett continually requested that they be enlisted. When the Congress brought the issue of declaration up to the Continental Congress, Bartlett was the first to say yes to the motion. He was also the first to sign the Declaration of Independence after John Hancock.
Josiah Bartlett retired from public service and would soon die on May 19, 1795. He was laid to rest next to his wife in Plains Cemetery in Kingston, New Hampshire.
Bartlett lived a full life and would discover Peruvian Bark that would alleviate the symptoms of throat distemper which would prove useful during an outbreak in the 1730s. Throat distemper was fatal to many, especially the young.