Shortly after the colonies declared their independence, Ingersoll renounced his family's views, made his personal commitment to the cause of independence, and returned home. In 1778 he arrived in Philadelphia as a confirmed Patriot. With the help of influential friends he quickly established a flourishing law practice, and shortly after he entered the fray as a delegate to the Continental Congress (1780–81). In 1781 Ingersoll married Elizabeth Pettit and in that same year was elected a member of the American Philosophical Society. Always a supporter of strong central authority in political affairs, he became a leading agitator for reforming the national government in the postwar years, preaching the need for change to his friends in Congress and to the legal community.