In Scotland he became famous representing the city of Edinburgh, when it was threatened with deprivation of rights, for the death of an English captain of the city guard, hanged by a mob. However, his English practice remained rare until 1737, when his eloquent speech before the House of Commons in support of merchants’ petition to stop Spanish aggressions on their ships, placed him in the forefront of his profession. In 1742 he was appointed attorney general. In 1754 he became attorney general and acted as head of the House of Commons under the Duke of Newcastle.
In 1756 he was appointed Chief Justice of the Royal Bank and was named Baron Mansfield, becoming Earl of Mansfield in 1776. Due to the limitations of his 1776 patent, he was granted a new patent in 1792, as Earl of Mansfield de Caen Wood.
In another case involving the prosecution of journalist John Wilkes, who had published works that were found defamatory and seditious by the House of Commons, Mansfield, ignoring the popular clamor and the real pressure, with a careful technical work of the antecedents. His investigations showed that the crown’s case contained legal flaws, and he felt compelled to release the agitator, because the process required it.
A legendary widely held opinion that Mansfield abolished slavery in England with a court decision, while the civil war in the United States was going on, it is unfounded. Like a wealthy man with a business mind, Mansfield he sought to avoid any problems with slavery. Even his sentence on the call Somersett case (1772), which involved the slave James Somersett, who was bought in Virginia and tried to flee after arriving in London, decided only that an escaping slave could not be forcibly removed from England to be punished in a colony.
The permanent seal of Mansfield in Anglo-American law he settled in commercial law. When he took office, at the start of the Seven Years’ War, it was to tighten the grip of Great Britain in America, India, and international trade. English law was centered on land and its properties and rooted in professional tradition. The reform was essential. The vision and ambition of Mansfield they went beyond the continental model of a special body of rules for commerce and banking. He tried to make International Trade Law not a separate branch of law, but an integral part of the general law of England.
In the field of bills of exchange (drafts), promissory notes, and the -by then still a novelty- bank check, MansfieldFollowing international standard practice, he modeled the law by investigating every relevant situation and its reasons. But Mansfield it also established a new area of ​​jurisprudence. Marine insurance, a new industry centered in London, was a weapon of competition and of the cold war. Mansfield did not build models here; created all discipline.
Three times during his career he held positions as a member of the Council of Ministers, entrusting the great seal of his office to a committee, so that he could retain the presidency of the court, regardless of changes in administration, but still exercise political power. In 1783 he rejected the cabinet office, preferring to serve as president of the House of Lords. He resigned the presidency of the Supreme Court in 1788.
He died on March 20, 1793, at the age of 88.