Isabella of Coimbra was born on 1 March 1432 as the daughter of Infante Peter, Duke of Coimbra and Isabella of Aragon, Countess of Urgell. Through her father, she was a granddaughter of King John I of Portugal.
Her father acted as regent for her cousin, King Afonso V of Portugal and she and Afonso reportedly fell in love with each other. Their engagement in 1445 angered Duke of Afonso of Braganza, who had wanted the King to marry one of his granddaughters (Isabella of Portugal, who later became the mother of Isabella I of Castile or Beatrice of Portugal, who married Infante Ferdinand, Duke of Viseu and became the mother of King Manuel I of Portugal)
Isabella and Afonso were married on 6 May 1447, and they went on to have three children, John, Prince of Portugal, who died young, Joan, Princess of Portugal (known as the Princess Saint) and the future John II of Portugal. Afonso took the Duke of Braganza as his advisor in 1448 and Isabella’s father died under suspicious circumstances, while her brother was exiled. Nevertheless, Isabella remained on her husband’s good side and managed the Duchy of Coimbra until her brother’s return in 1454. Isabella had her father honoured in 1455 and reburied him in a grand ceremony. She died not much later, at the age of 23, also under suspicious circumstances.
She is buried in the Batalha Monastery.
After her death, her husband married his niece Joanna la Beltraneja, who would have been the heiress of Castile had her paternity not been doubted.