Following the Battles of Lexington and Concord, he left his medical practice in Georgetown (now Bath) Maine to serve his newly forming country in his home state of Massachusetts.
At which point he remained in the service of his country as a reserve surgeon to Col Henry Jackson's Regiment after the war.
It was at this point he took it upon himself to pay the men directly from that money, and was summarily chastised by Congress for this "reprehensible act".
After serving a total of 9 years and 3 months, Hart returned to Middlesex County and settled in Reading Township.
It was here he opened his personal medical practice and soon was the doctor for the entire region (including Essex and Suffolk counties).