Pinckney was born into a powerful family of aristocratic planters. He practiced law for several years and was elected to the colonial legislature. A supporter of independence from Great Britain, Pinckney served in the American Revolutionary War, rising to the rank of brigadier general. After the war, he won election to the South Carolina legislature, where he and his brother Thomas Pinckney represented the landed elite of the South Carolina Lowcountry. An advocate of a stronger federal government, Pinckney served as a delegate to the 1787 Philadelphia Convention, which wrote a new federal constitution. Pinckney's influence helped ensure that South Carolina would ratify the United States Constitution.