English Roman Catholic priest, notable for his criticisms of several of the leading thinkers of his time, including John Locke.

After serving as secretary to Thomas Morton, Anglican bishop of Durham, Sergeant was converted to Roman Catholicism. He then took theological studies at the English College, Lisbon, was ordained (1650) and was sent on the English mission in 1652 to defend the Catholic cause. His uncompromising attitude, however, ruined his ambition to restore the toleration of Catholic worship and ecclesiastical authority in England. In 1675 he lived in France.

Theological and philosophical controversy occupied most of Sergeant's life. Among his adversaries were the English clergyman and writer Jeremy Taylor and Archbishop Peter Talbot of Dublin, who labelled certain of Sergeant's writings heretical. Sergeant attacked Locke (Locke, John) in his Solid Philosophy Asserted, Against the Fancies of the Ideists (1697). He held that knowledge can be extended and explained by resorting to metaphysical and general principles of reason (or “maxims”) when empirical investigations yield no new knowledge. He therefore criticized Locke, who denied the importance of these principles in extending knowledge, though he did not rule them out entirely.