John Sergeant graduated from Princeton College and was admitted to the bar, beginning a career in law. He held various legal and governmental positions, including Deputy Attorney General for Philadelphia and Commissioner of Bankruptcy for Pennsylvania. Sergeant served multiple terms in the Pennsylvania State House of Representatives and the United States House of Representatives, where he chaired the Committee on the Judiciary. He also held leadership roles in the public sector, such as President of the Pennsylvania Board of Canal Commissioners. Throughout his career, Sergeant maintained a strong commitment to legal practice and public service.

John Sergeant's political identity is marked by a unique blend of economic nationalism and principled abolitionism. He was a fervent advocate for Henry Clay's American System, yet his opposition to the Missouri Compromise reveals a complex stance on slavery that defies simple categorization. Sergeant's legislative record shows an unexpected convergence with opposing factions on environmental regulations, revealing a highly calculated approach to protecting regional industrial interests. His rhetorical style emphasizes legal rigor and constitutional fidelity, often framing issues through a judicial lens.