Alvares Pereira was born in June 24 1360 in the village of Cernache, central Portugal. When king Fernando of Portugal died in 1383, with no heir besides Beatrice married to king Juan I of Castile, he was one of the first nobles to support the claim of D. Joćo, Master of Aviz to the throne. True that he was a bastard son of Pedro I, but, like many others, it was a better option than the loss of independence. After his the first victory over the Castilians, in the battle of Atoleiros (April 1384), Joćo of Aviz names Alvares Pereira protector and general of the kingdom (Condestįvel do Reino) and Count of Ourém.
In April 1385, Joćo is recognized and accepted as king by the kingdom assembly (the Cortes). This strong Portuguese position for independence triggers an invasion of the country by Juan of Castile, willing to defend his wife's rights to the throne. Alvares Pereira engages in a pursuit against the cities loyal to the Castilians, namely in the North of the country. In August, he was the mastermind of the Portuguese victory in the battle of Aljubarrota, after which the threat of annexation was over. After the 1383-1385 Crisis, Alvares Pereira received from Joćo I the titles of Count of Arraiolos and Count of Barcelos.
Not wanting to give the enemy room to manoeuvre, Joćo I and his favourite general raided several Castilian towns and continued to watch out for John I of Castile, until his death in 1390.
Alvares Pereira died peacefully in the Convent of Carmo in Lisbon in November 1 1431 and his reminded as one of the most successful Portuguese generals.
He sired only one daughter, Beatrice, from his marriage to Leonor de Alvim, which was to become the wife of Afonso, the first duke of Braganēa.