Robert Treat Paine (March 11, 1731–May 11, 1814), was a signer of the United States Declaration of Independence as a representative of Massachusetts.
He was born in Boston, Massachusetts and attended Boston Latin School. He graduated from Harvard College in 1749, then taught school and studied theology. He became a merchant marine and traveled to the southern colonies, Spain, the Azores, and England. He returned home, and was admitted to the bar of Massachusetts in 1757 or 1759, practicing in Portland, then part of Massachusetts (but now in Maine), and later in Taunton, Massachusetts.
In 1768 he was a delegate to the provincial convention which was called to meet in Boston, and conducted the prosecution of Captain Thomas Preston and his British soldiers following the Boston Massacre of March 5, 1770
He served in the Massachusetts General Court from 1773 to 1774, in the Provincial Congress from 1774 to 1775 represented Massachusetts at the Continental Congress of 1776. (He served in the Continental Congress from 1774 through 1778 and helped frame the rules of debate and acquire gunpowder for the coming war). He signed the final appeal to the king (the Olive Branch Petition) in 1775.
He was speaker of the Massachusetts House of Representatives in 1777, a member of the executive council in 1779, a member of the committee which drafted the constitution of 1780, Massachusetts Attorney General from 1777 to 1790, and a judge of the state supreme court from 1790 to 1804, and retired dying at the age of 83.