Katharina war das vierte Kind des portugiesischen Königs Johann IV. (1604-1656) und dessen Gattin Luisa von Guzmán (1613-1666). Sie erblickte das Licht der Welt am 25. November 1638 und starb am 31. Dezember 1705. Im Jahr 1662 hatte sie den englischen König Karl II. Stuart (1630-1685) zu heiraten. Aus ihrer Ehe gingen keine Kinder hervor.
Ihr Geburtstag am 25. November war ein ganz besonderer Tag in Portugal, denn an diesem Tag konnte sich Portugal im Jahr 1640 vom spanischen Joch befreien: "From that era, the twenty-fifth of November 1640, Portugal became an independent sovereignty, after having been for sixty years an appanage of Spain. Immediately after John the Fourth had defeated the Spanish forces in 1640, Charles the First recognized him as sovereign of Portugal, a service refused to him by the Pope, and by all the Catholic courts of Europe, excepting France, and which emboldened him to propose, through his Ambassador, the marriage of his daughter, Katherine of Braganza, with the Prince of Wales, afterwards Charles the Second; a proposal to which the needy English monarch listened with stoical indifference. Katherine was educated in a convent, under the immediate superintendence of her wise, energetic mother … and in November, 1654, her father, out of the unbounded affection he bore her, gave her, besides other sources of income, the island of Madeira, the city of Lanega, and the town of Mour; but with a proviso, that if she married out of the kingdom, she should exchange them for a suitable equivalent from the nation. Shortly afterwards her father died, and her eldest brother [nicht korrekt: ihr ältester Bruder war Teodosio (1634-1653)], Don Alphonso, being too young to reign, her mother assumed the regal authority, which she exercised for ten years [nicht korrekt: ihre Mutter war dessen Regentin bis 1662, also acht Jahre lang], with such success, that the independence of Portugal was firmly established, the commerce and trade of the nation enlarged, and the social condition of the people greatly meliorated." (in: Francis Lancelott: The Queens of England and their Times, Volume II, id., pp. 710-711).
"Don Francisco del Mello, the Portuguese Ambassador in England ... proposed the match to the King’s Lord Chamberlain, the Earl of Manchester, [im Jahr 1660] and on the following day paid Charles [Karl II. Stuart] a visit in person, and offered with the Princess a dower of five hundred thousand pounds in ready money, and to annex Tangiers, on the coast of Africa, and Bombay, in the East Indies, to the crown of England for ever; and to grant to the English a free trade to Portugal and to the Portuguese colonies. Charles, who greatly needed money [war zu dieser Heirat bereit]. ... At the commencement of 1661, he [der portugiesische Botschafter Francisco del Mello] arrived at London, when, to his surprise, he was received with great coolness at court; in fact, in his absence, Vatteville, the Spanish Ambassador, had informed Charles, that Katharine was known to be incapable of becoming a mother; she was ugly and deformed, and his marriage with her would lead to a war with Spain and other evils; but if he would take one of the Princesses of Parma, the King of Spain would give with either of those ladies as large a dower as would be given with a daughter of Spain. These suggestions … induced Charles to dispatch that nobleman [the Earl of Bristol] to Parma, to obtain information regarding the two Princesses [Maria Caterina (1637-1684) und Maria Maddalena (1638-1693)]. He saw them on their way to church; the one sight convinced him that the one was too ugly, the other too corpulent, to be recommended to the royal choice." (in: Francis Lancelott: The Queens of England and their Times, Volume II, id., pp. 711-712).
"Following the signing of the marriage treaty with Charles II, she landed at Portsmouth on 14 May 1662 with a large Portuguese retinue. The marriage was a political and dynastic one, and her Catholicism made her unpopular in Britain. Throughout the 1660s … Catherine suffered several miscarriages… although she is noted as showing kindness to her husband’s illegitimate children. The diarist and writer John Evelyn (1620-1706) remarked on 'her pretty shape', 'languishing and excellent eyes' and projecting teeth; shy and solemn, she was devoted to her husband, and, although he hurt her by his infidelities, he had a genuine affection to her." (in: D. Piper: Catalogue of Seventeenth-Century Portraits in the National Portrait Gallery, 1625-1714, Cambridge 1963, pp. 56-57).