Petty was briefly a Member of the Parliament of England and was also a scientist, inventor, and merchant, and was a charter member of the Royal Society. It is for his theories on economics and his methods of "political arithmetic" that he is best remembered, however, and to him is attributed the philosophy of "laissez-faire" in relation to government activity. He was knighted in 1661. He was the great-grandfather of Prime Minister William Petty Fitzmaurice, 2nd Earl of Shelburne and 1st Marquess of Lansdowne.