Derek Mills-Roberts was born on 23 November 1908 in England. During the 1930s, he trained to become a lawyer at Liverpool College and University of Oxford. On 3 October 1936, he was commissioned into the Irish Guards Supplementary Reserve of Officers as a second lieutenant, having been an officer cadet of the University of Oxford contingent of the Officer Training Corps. It was at Oxford that Derek met his good friend Lord Lovat. Derek and Lord Lovat had actually got off on a bad start. They had a rivalry which involved a heated argument and an exchange of blows. From that time on however, they became close friends. After graduation from Oxford, Derek worked for his father's law firm.