He was born in London; his father was the Spanish journalist Felipe Fernández Armesto (who wrote using the pseudonym Augusto Assía [es]) and his mother was Betty Millan, a British-born journalist and co-founder (with Remy Hefter, in 1947) and editor of The Diplomatist (whose current title is Diplomat), the in-house journal of the diplomatic corps in London.
He began his teaching career at Charterhouse School in Godalming, Surrey.
In 1982 he published The Canary Islands after the Conquest: The Making of a Colonial Society in the Early Sixteenth Century, an archival study of the Canary Islands during the period of their original settlement.
In 1987 he published Before Columbus: Exploration and Colonization from the Mediterranean to the Atlantic 1229–1492, a study of the earliest phase of European imperialism when Europeans left the Mediterranean and colonized the islands along the northwest coast of Africa.
[2][3] Among other distinctions, Fernández-Armesto has won the John Carter Brown Medal, the Caird Medal of the National Maritime Museum (UK), the Premio Nacional an Investigacion of the Sociedad Geográfica Española, Spain's Premio Nacional de Gastronomia for his history of food, and the Tercentenary Medal of the Society of Antiquaries of London.