Hartley William Shawcross was born to John and Hilda Shawcross in Germany, whilst his father was teaching English at Giessen University. He was educated at Dulwich College, the London School of Economics and University of Geneva and sat for the Bar at Gray's Inn, where he won first-class honours. He was the youngest man ever to be made King's Counsel.
He joined Labour at a young age, and served as Member of Parliament from St Helens from 1945 to 1958, holding the position of Attorney-General from 1945 to 1951. It was in 1946 when debating the repeal of anti-Union laws in the House of Commons that Shawcross made the "We are the masters at the moment" comment (widely misquoted as "We are the masters now") that came to haunt him.
As Attorney-General, he prosecuted William Joyce ("Lord Haw-Haw") and John Amery for treason and also prosecuted Klaus Fuchs and Alan Nunn May, for giving atomic secrets to the Soviet Union and John George Haigh (the acid bath murderer) for murder. He was knighted in 1945 and named Chief Prosecutor for the United Kingdom at Nuremberg. From 1945 to 1949, he was Britain's principal United Nations delegate and in 1951, he briefly served as President of the Board of Trade until the Labour government's defeat in the election of that year. He ended his law career in 1957, and resigned from Parliament in 1958, saying he was tired of party politics. He was made a life peer on February 14, 1959 as Baron Shawcross, of Friston, Sussex, and sat in the House of Lords as a cross-bencher.
He was instrumental in the foundation of the University of Sussex and was served as chancellor of the university from 1965 to 1989.
Lord Shawcross was married three times. His first wife Alberta Rosita Shyvers (m. May 24, 1924) suffered from multiple sclerosis and committed suicide on December 30, 1943. His second wife Joan Winifred Mather (m. September 21, 1944) died in a riding accident on the Sussex Downs on January 26, 1974. At the age of 95 he married Mrs. Susanne Monique Huiskamp on April 18, 1997 in Gibraltar.
He had a son, (the author and historian William Shawcross) and daughter Joanna by his second wife.
He died at home at Cowbeech, East Sussex at the age of 101.
Shawcross' advocacy before the Nuremberg Trial was devastating. His most famous line was:
Shawcross and the Nuremberg Trials
Shawcross avoided the crusading style of Americann, Russiann and French prosecutors. Shawcross opening speech, which lasted two days, was able to undermine any belief that the Nuremberg Trials were a victor's justice, an exacted vengeance against defeated foes. Instead, Shawcross focussed on the rule of law. Shawcross demonstrated to the court that the laws the defendants had broken had been expressed in international treaties and agreements pre-dating the war, and to which Germany was a party.
On the question of conscience, in his closing speech Shawcross ridiculed any notion that any of the defendants could have remained ignorant of thousands of Germans exterminated because they were old or mentally ill. Shawcross used the same argument for the millions of other people "annihilated in the gas chambers or by shooting". Shawcross maintained that each of the 22 defendants was a party to "common murder in its most ruthless forms".
Shawcross' advocacy was instrumental in obtaining convictions against the remaining Nazi leadership on grounds which were perceived as fair and lawful.