Born in Scone Palace, Perthshire, to a family of Scottish nobility, he was educated in Perth before moving to London at the age of 13 to study at Westminster School.

Accepted into Christ Church, Oxford, in May 1723, Mansfield graduated four years later and returned to London, where he was called to the Bar by Lincoln's Inn in November 1730 and quickly gained a reputation as an excellent barrister.

In the absence of a strong Attorney General, Mansfield became the main spokesman for the government in the House of Commons, where he was noted for his "great powers of eloquence" and was described as "beyond comparison the best speaker".

[6][7] Both his parents were strong supporters of the Jacobite cause,[8][9] and his older brother James followed the "Old Pretender" into exile, this left the family's finance relatively impoverished.

When Mansfield's other nephew, Sir John Lindsay, returned to Britain in 1765 following the Seven Years' War and his assignment in the West Indies, he brought his illegitimate daughter, Dido, whose mother, Maria Bell, was an enslaved woman of African descent.

[21][22] There was no formal legal education at this time, and the only requirement for a person to be called to the Bar was for him to have eaten five dinners a term at Lincoln's Inn, and to have read the first sentence of a paper prepared for him by the steward.

[23] Thus, most of Murray's practical training came from reading the papers in Hamilton's chambers, and listening to Lord Raymond speak in court[23] along with tutoring by Thomas Denison on how to write special pleadings.

[22] Murray also studied various texts, including the French Ordinance de la Marine (a predecessor to the Napoleonic Commercial Code), the works of Bracton and Littleton, and "crabbed and uncouth compositions" on municipal law.

Lady Stormont may have provided Murray with some financial support while he was a law student, on top of sending him food packages, including his favorite Scottish marmalade, when he was a young lawyer.

Some of the aristocrats thought that the bride had married way below her status, and they also accused the groom (at the time just Mr. Murray) of social climbing into one of the great English families which the Finches belonged to.

[32] His argument (that it was the prerogative of the King to decide how a war should be fought, and he should not be second-guessed by politicians with no experience of warfare) defeated the motion to cease employing the Hanoverian troops by 231 votes to 181.

[37] His Scottish and Jacobite roots also allowed for endless insinuation and controversy—in 1753 he was accused by James Johnson Bishop of Gloucester of "having drunk the health of the Old Pretender on his knees".

[37] It was widely felt that he could have become Prime Minister after the death of Henry Pelham, but it would have "set [his genius] in a false environment", and he declined all opportunities to return to politics except as Lord Chief Justice.

[41] The legal system had been put together in the period immediately after the Norman conquest of England, and was completely unsuited to the 18th century, when Britain was "the greatest manufacturing and commercial country in the world".

Mansfield also enforced a previous judgement of the Court of King's Bench made in 1645, in which they allowed a special jury of merchants to sit in cases involving commercial law.

[54] In 1783, Mansfield heard the case of Gregson v. Gilbert (1783) 3 Doug 232, 99 ER 629, regarding the payment of an insurance claim for slaves killed when thrown overboard by the captain of a slave-ship – an event now known as the Zong massacre.

After the term of the exclusive rights granted under the Statute of Anne expired, Robert Taylor began publishing his own competing publication, which contained Thomson's poem.

[56] Mansfield's judgment has been criticised as being unusually short-sighted because he failed to see that while his decision was correct for that particular case, the precedent it would set would create an unfair monopoly for the booksellers and publishers.

[60] From 21 November 1768, letters written by a man under the pseudonym of Junius were published in the Public Advertiser, a London newspaper run by Henry Sampson Woodfall.

[62] On 14 November 1770, a letter by Junius directed at Mansfield was published by the Public Advertiser and the London Evening Post, a newspaper run by John Miller.

[65] In the meantime, the case had attracted a great deal of attention in the press, and members of the public were forthcoming with donations to fund lawyers for both sides of the argument.

[69] Finally, on 22 June 1772 Mansfield gave his judgment, which ruled that a master could not carry his slave out of England by force, and concluded: The state of slavery is of such a nature, that it is incapable of being introduced on any reasons, moral or political; but only positive law, which preserves its force long after the reasons, occasion, and time itself from whence it was created, is erased from memory: it's so odious, that nothing can be suffered to support it, but positive law.

)[71] Mansfield believed that his decision meant that slavery continued, because his mixed-race great-niece Dido Elizabeth Belle remained a slave in his household, until his 1793 will allowed her to be considered a free woman.

The term "Lord Mansfield's Rule" is often used in a slightly different sense to denote the principle still applied in several jurisdictions[82] that marriage creates a conclusive presumption of a husband's paternity of his wife's child.

[85] In an attempt to speed up the process of passing the bill, Mansfield left his position as speaker to debate directly on 15 December; when this failed to help he returned to the Woolsack the next day.

"[98] He made his judgements on the principle that "as the usages of society alter, the law must adapt itself to the various situations of mankind", leading John Baker to describe him as "one of the boldest of judicial spirits".

[103] Various comments he made before and during the case also suggest that complete emancipation was not his intent; in a preliminary judgment he said that "the setting 14,000 or 15,000 men at once free loose by a solemn opinion, is much disagreeable in the effect it threatens", which one modern legal scholar interprets as indicative of his reluctance to make a decision for fear of economic consequences.

From the love which he bore to the place of his early education, he desired to be buried in this cathedral (privately) and would have forbidden that instance of human vanity, the erecting a monument to his memory, but a sum which with the interest has amounted to two thousand five hundred pounds was left for that purpose by A. Bailey Esqr.

[111] He was summarised by Gareth Jones as "Conservative, urbane, silver-tongued, energetic, cultivated and well read; a highly imaginative lawyer who looked to reason and was not overawed by the legacy of the past".

[11] Mansfield has been called "the legal genius of his generation",[117] and compared favourably with Joseph Story, a judge of the Supreme Court of the United States noted for his brilliance.