He read law and was admitted to the bar in 1778, and then moved to York in Massachusetts' District of Maine to open a practice.

In 1788 North Carolina passed a law allowing the capture and sale of any former slave who had been freed without court approval.

Many freed African Americans fled the state to avoid being captured and sold back into slavery.

[7] Thatcher, an ardent Unitarian, helped to sponsor the creation of Bowdoin College so that Maine would have its own institution of higher education.

Thatcher was elected a member of the American Antiquarian Society in 1814,[8] and served on its board of councilors from 1815 to 1819.