He was born in London, his father was the Spanish journalist Felipe Fernández Armesto and his mother was Betty Millan de Fernandez-Armesto, a British-born journalist and co-founder and editor of The Diplomatist, the in-house journal of the diplomatic corps in London. Fernández-Armesto is Professor of Global Environmental History at Queen Mary, University of London, and a member of the Faculty of Modern History at Oxford University.
From September 2005, he has been Principe de Asturias Chair in Spanish Culture and Civilization at Tufts University.
Fernández-Armesto gained media attention in 2007 for an incident on January 4th in which he was allegedly brutalized by 5 policemen led by Kevin Leonpacher in Atlanta, Georgia as a result of jaywalking while in town for a conference of the American Historical Association. When told by 28-year-old officer Leonpacher that he was not supposed to cross where he had, he said he simply thanked him and continued on, claiming not to have known that Leonpacher was an officer because he was wearing a "bomber jacket" which covered his badge and obscured the uniform that Leonpacher claimed to have been visibly wearing. When Leonpacher ordered him to produce identification, the 56-year-old responded by questioning his authority to make such a demand and in turn, requesting to see the officer's ID. Upon asking that Leonpacher show him his credentials, he was subsequently "knocked", "thrown and/or "wrestled" to the ground after having his legs kicked from under him, and pinned there by the officers. Professor Lisa Kazmier, who witnessed the incident, was quoted as saying "It was like he was Osama Bin Laden or something. Leonpacher and the Atlanta Police Department deny that unnecessary or inappropriate measures were taken. After having been arrested and jailed for eight hours, Fernández-Armesto was released and charges of "disorderly conduct" against him were unofficially dropped following an appearance in traffic court the next day. Despite having once been mugged, he stated that "It was the most violence I've ever experienced in my life".
Officer Leonpacher has a different version of the events in the article "Officer Says He Used Discretion Before Arresting Prof". The five-year Atlanta Police Department veteran said when he asked Fernandez-Armesto why he didn't follow his instructions not to jaywalk, the author shrugged him off and walked away."Five times I asked him to stop," the officer said. He then asked him if he was hearing impaired. Once Fernandez-Armesto confirmed he wasn't, Leonpacher said he grabbed the professor's arm. "I let him go when he turned around to face me," he said. Leonpacher then says he repeatedly asked Fernandez-Armesto for his identification, but the professor responded by asking for the officer's I.D. When the historian allegedly repeatedly refused to produce ID, Leonpacher said he told him he was under arrest. The historian began to wrestle Leonpacher. "He was swinging, kicking wildly," Leonpacher said. Backup was called to assist in his detainment.