Portuguese Roman Catholic wife of King Charles II of England (ruled 1660–85). A pawn in diplomatic dealings and anti-papal intrigues, she was married to Charles as part of an important alliance between England and Portugal.

Catherine's father became King John IV of Portugal in 1640. Her marriage, which took place in May 1662, brought England valuable trading privileges and the port cities of Tangier (in Morocco) and Bombay. In return, England pledged to help Portugal maintain its independence from Spain.

The young queen had little personal charm, and, despite her deep affection for Charles, he paid less attention to her than to his mistresses. When it became apparent that she would bear the King no children, opponents of his brother, James, duke of York, urged him to divorce her in the hope that Charles could then be induced to wed a Protestant. In 1678 they accused Catherine of scheming to poison the King and place his Roman Catholic brother James on the throne. But Charles, who never doubted his wife's innocence, stood by her until she was cleared of the charges. Catherine helped convert Charles to the Roman Catholic Church shortly before he died in 1685, and in 1692 she returned to Portugal. In 1704 she became regent of Portugal for her ailing brother, King Pedro II.