Katharina traf am 14. Mai 1662 mit ihrer großen portugiesischen Gefolgschaft in Portsmouth ein. In ihrem neuen Königreich war sie als Katholikin nicht beliebt. Ihren Gatten, den englisch-schottischen König Karl II. Stuart, liebte sie sehr, aber seine vielen außerehelichen Affären taten ihr sehr weh. Trotzdem war sie gegenüber seinen vielen unehelichen Kindern stets sehr freundlich. Sie selbst erlitt in den 1660er Jahren viele Fehlgeburten und blieb ohne ein eigenes Kind.
Über ihre Mitgift lesen wir Folgendes: "But what really won his [Karls II.] heart was the size of her dowry - some £300,000 in cash, the island of Bombay and the port of Tangier, together with valuable trading privileges for English seamen in the New World." (in: Christopher Falkus: The Life and Times of Charles II, p. 89).
Karl II. traf in Portsmouth am 20. Mai 1662 ein. Er schrieb Edward Hyde: "It was happy for the honour of the nation I was not put to the consummation of the marriage last night, for I was so sleepy, by having slept but two hours in my journey, that I was afraid that matters would have gone very sleepily. I can only now give you an account of what I have seen a-bed; which, in short, is; her face is not so exact as to be called a beauty, though her eyes are excellent good, and not anything in her face that in the least can shock one. On the contrary, she has much agreeableness in her looks altogether as ever I saw; and, if I have my kill in physiognomy, which I think I have, she must be as good a woman a ever was born ... You would much wonder to see how well we are acquainted already." ... "The couple was married on 21 May, secretly according to Catholic rites for the Queen's sake, and publicly by the Bishop of London. Catherine could speak no English, and her convent upbringing scarcely equipped her for the court of the merry monarch. Her retinue of monks and forbidding-looking ladies caused much amusement to the gay courtiers who surrounded the King." (in: Christopher Falkus: The Life and Times of Charles II, p. 90).
Katharina von Braganza war aber nicht bereit, Barbara Villiers, die bekannte Geliebte ihres Gatten, als ihre Hofdame zu akzeptieren. Diesen Kampf verlor sie gegenüber ihrem Gatten: "In this struggle Charles used a variety of tactics. Once he openly introduced his mistress at court, and when Catherine learnt who it was who had just kissed her hand she fainted. Then Charles began to ignore her, and plunged himself even more vigorously into his other pleasures. He had her Portuguese ladies sent home, and left her an isolated figure, friendless and helpless in her misery. Then, quite suddenly, Catherine gave up the unequal fight and not only accepted Lady Castlemaine [Barbara Villiers neuer Titel] but went out of her way to pay her compliments and cultivate her as a friend. She began to compete for the King's affections, cutting her dresses lower and her skirts shorter, Charles responded, and for the rest of the reign domestic harmony prevailed." (in: Christopher Falkus: The Life and Times of Charles II, pp. 90-91).