 He was educated at Winchester, Oxford and Law and History at the University of Leiden (1765-1767).Harris arrived in Spain in December 1768 and became secretary to the British embassy at Madrid, and was left as "chargé d'affaires" at that court on the departure of Sir James Grey in August 1769 until the arrival of George Pitt, afterwards Lord Rivers.This interval gave him his opportunity; he discovered the intention of Spain to attack the Falkland Islands, and was instrumental in thwarting it by putting on a bold countenance.