She was the second daughter of Infante Duarte, Duke of Guimarães (sixth son of Manuel I of Portugal) and Isabel of Braganza, she was married to Duke John I of Braganza, a descendant of earlier Portuguese monarchs, and head of the most important aristocratic House in Portugal. The duchess had several children, of whom Teodósio de Braganza, was her eldest surviving son.
Catarina of Portugal was the younger daughter of Duarte, Duke of Guimarães, king Henry's youngest brother, and his wife Isabel of Braganza. When King Henry died (1580), Duarte's issue were the only surviving legitimate heirs of any of the sons of King Manuel I of Portugal. As the male line is preferred in Portuguese succession before the female one, descendants of Manuel I's daughters (such as king Philip II of Spain) had, in principle, only a weaker claim to the throne than Duarte's descendants, to whom Catherine belonged.
Following this principle, the first in line to the throne would have been Catherine's nephew Ranuccio I Farnese of Parma, as that 11-year old Italian boy was the heir of her elder sister Maria of Guimarães. Catherine is said to have been ambitious and participated in intrigues.
Her cousin Philip II of Spain used his descent as son of Infanta Isabella, eldest daughter of king Manuel I. And, her other cousin António, Prior of Crato was a male, though illegitimate. António had already in 1578 claimed the throne.
Catherine had married the Duke of Braganza, John, who himself as a grandson of the late Duke Jaime, Duke of Braganza was a legitimate heir of Portugal. The Duchess' son, D. Teodósio de Braganza, would have been their royal heir and successor to the throne.
The duchess's claim was relatively strong, as it was reinforced by her husband's position as one of the legitimate heirs; thus they would both be entitled to hold the kingship. Her claim was also strengthened by the fact that she was living in Portugal, and was a mature woman of forty. However, Portugal had not yet had a generally recognized queen regnant, but only males on the throne. Moreover, she was a younger daughter, thus there was a genealogically senior claimant, her nephew Ranuccio.
She failed in the struggle: the strongest claimant was her cousin Philip II of Spain who wanted to unite Portugal in a personal union with the other Spanish kingdoms under himself. The nationalist party, those who desired Portugal to remain independent, supported her illegitimate cousin António of Crato, not Catherine. António lost the final competition to Philip in the Battle of Alcântara in 1580.
In a couple of years, she lost her husband João of Braganza (1543-1583). She lived on as a widowed lady under the rule of her Castilian cousin.
In 1640, Catherine's grandson and direct heir, the then Duke of Braganza, became King John IV of Portugal. The Duchess was then retrospectively acknowledged as the legitimate heir, as result of her descendants obtaining the throne, although in her own lifetime she was only one of several possible heirs. By the unanimous voice of the people John was raised to the throne of Portugal during the revolution effected on December 1, 1640 against the Spanish king, Philip IV.
Catherine and her husband had the following children: