He was born in Crato, Portugal and raised as a New Christian. He was driven away from Portugal by the Portuguese Inquisition and was considered a Marrano (a hidden Jew). He made London his home in 1559 and successfully resumed his practice as a doctor, soon becoming house physician at St. Bartholomew's Hospital. Despite prejudice and professional jealousy, he developed a large practice among powerful people, including Robert Dudley and Francis Walsingham. Rumor held that his success was less due to his medical skill and more to his skill at flattery and self-promotion. A 1584 libelous pamphlet attacking Dudley suggested that López distilled poisons for Dudley and other noblemen as well. In 1586, López reached the pinnacle of his profession; he was made physician-in-chief to Queen Elizabeth