Mary I's accession in 1553 followed a struggle over the succession after Edward VI attempted to exclude her in favor of Lady Jane Grey. Mary rallied support, secured recognition, and became the first woman to exercise sustained rule as England's reigning monarch. Her immediate program restored Catholic worship and reversed Protestant measures enacted under her half-brother. Parliament and Cardinal Reginald Pole later helped reestablish formal communion with Rome, while arrangements protected many existing owners of former monastic lands.

Mary's marriage to Philip of Spain in 1554 raised fears of foreign domination. The marriage treaty limited his powers in England, but opposition contributed to Wyatt's Rebellion. Mary did not surrender her governing authority to Philip, though his dynastic interests and absences complicated their partnership. Her hoped-for pregnancies produced no surviving child, leaving the succession and the durability of religious restoration uncertain.

The revival of heresy laws led to the burning of approximately 280 Protestants from 1555, including Archbishop Thomas Cranmer, Hugh Latimer, and Nicholas Ridley. These executions were intended to restore religious uniformity but created martyrs whose stories became central to later Protestant memory. The persecution forms an essential part of her reign and should not be minimized as merely a hostile later invention. At the same time, the nickname Bloody Mary can obscure the wider administrative, fiscal, and political work of her government and the coercive religious practices of the period.

Mary's administration pursued revenue and naval improvements while facing poor harvests, disease, and financial pressure. Alliance with Spain drew England into war against France, and the loss of Calais in 1558 was a major blow to prestige. She died later that year and was succeeded by Elizabeth, whose government again changed the religious settlement. Mary's career demonstrated that a woman could command support and exercise the powers of the English crown, but her principal religious objective did not survive her reign. A balanced assessment includes the succession victory, institutional work, and constraints of an unprecedented position alongside persecution, failed dynastic hopes, and costly foreign policy. Her legacy was shaped especially by the Protestant settlement that followed and by competing interpretations of Catholic restoration.