Born in County Antrim, Ireland, Paterson moved to the North American British colonies at a young age. After graduating from the College of New Jersey (now Princeton University) and studying law under Richard Stockton, he was admitted to the bar in 1768. He helped write the 1776 Constitution of New Jersey and served as the New Jersey Attorney General from 1776 to 1783. He represented New Jersey at the 1787 Philadelphia Convention, where he proposed the New Jersey Plan, which would have provided for equal representation among the states in Congress.