Isaiah Berlin was born on June 6, 1909, in Riga, Latvia, to Mendel and Marie Berlin. His father was a timber merchant. The family left Riga when Isaiah was 6 years old, and in Petrograd (now St. Petersburg), Russia, the youngster witnessed the beginnings of the Russian Revolution. In 1920 the Berlins moved to England. When the family arrived in the country in March, he spoke very little English, but three months later he won an essay contest in his new language. He studied at St. Paul's School in Hammersmith and won a scholarship to Corpus Christi College of Oxford University. He received his degree in 1931 with first-class honors in humane letters, philosophy, politics, and economics, and he earned a master's degree in 1935.

Berlin was a lecturer in philosophy at New College, Oxford, beginning in 1932. During that same year he passed the examination making him a fellow of Oxford's All Souls College, making him the first Jew thus honored. In 1938 he was elected a fellow of New College, and he remained there as a fellow and lecturer until 1950.

During World War II, Berlin worked at the British Information Services office in New York, and he later served as the first secretary at the British embassy in Washington D.C., where he remained until 1946 except for a brief stint at the British embassy in Moscow in 1945. Prime Minister Winston Churchill was said to have enjoyed reading Berlin's summaries of United States opinion so much that he invited Berlin to lunch at 10 Downing Street, but the invitation was mistakenly delivered to the composer Irving Berlin.

In 1946 Berlin returned to his professorship at New College, but his study shifted from philosophy to the history of ideas. Intellectual history and political theory became new disciplines in themselves largely because of Berlin's pioneering work. In 1957 he was knighted by Queen Elizabeth II. That same year he was named Chichele professor of social and political theory at Oxford. Berlin was named master, or head, of the newly formed Wolfson College of Oxford in 1966, and he remained in that post until 1975, when he became an honorary fellow of Wolfson College. Berlin also lectured at colleges and universities around the world, including Harvard, Bryn Mawr, the University of Chicago, Princeton, the City University of New York, and the Australian National University in Canberra.

Berlin published his first book, ‘Karl Marx: His Life and Environment', in 1939. The book was praised for Berlin's scholarship as well as for his penetrating psychological and intellectual portrait of his subject. His translations of the works of Russian author Ivan Turgenev, beginning in 1950, were highly regarded, and one was produced as a play in London decades later. His other works were primarily lectures that were transcribed later as books, notably ‘The Hedgehog and the Fox' (1953), which became one of Berlin's most quoted pieces. Inspired by the observation of the ancient Greek writer Archilochus that “the fox knows many things, but the hedgehog knows one great thing,” Berlin sought to examine how this fundamental difference in perception shaped the ideas of some of history's most important thinkers. With history's “foxes,” Berlin grouped such thinkers as Leo Tolstoi, Aristotle, and James Joyce because of their devotion to depicting the subtle differences, as well as the sharp contradictions, that influenced the development of human history and thought. With the historical “hedgehogs,” Berlin grouped those thinkers whose single-minded pursuit of one idea or concept defined their entire worldview. In this group, Berlin included Fedor Dostoevski, Plato, Dante, and Karl Marx.

Among Berlin's most important essays were ‘Historical Inevitability' (1955), ‘Two Concepts of Liberty' (1959), and ‘Four Essays on Liberty' (1969). These works were considered Berlin's finest arguments defending liberty, free will, and pluralism against romantic and utopian philosophical systems. Other works included ‘The Age of Enlightenment' (1956); ‘Chaim Weizmann' (1958); ‘The Life and Opinions of Moses Hess' (1958); and ‘The Magus of the North' (1993). Some of his collected writings were published with the help of Henry Hardy, at the time a graduate student. The collections included ‘Russian Thinkers' (1978); ‘Against the Current' (1979); ‘The Crooked Timber of Humanity' (1990); and ‘The Sense of Reality' (1996).

In 1945, in recognition of Berlin's wartime service, he was named Commander of the Order of the British Empire. In 1957, Berlin was elected a fellow of the British Academy, and from 1974 to 1978 he served as president of the academy. He was made a member of the Order of Merit by Queen Elizabeth II in 1971. Berlin also served as a foreign member of the American Academy of Arts and Sciences, the American Academy-Institute of Arts and Letters, and the American Philosophical Society. During his lifetime, Berlin was awarded the Lippincott and Erasmus prizes (1983), the Agnelli International Prize for Ethics (1987), and the Jerusalem prize for his work on behalf of civil liberty. Berlin also received honorary doctorates from more than 20 universities and colleges, including Glasgow and Cambridge in the United Kingdom; Columbia, Harvard, and Yale in the United States; and Jerusalem and Tel Aviv in Israel.

Having written and lectured about totalitarianism, liberalism, renaissance thinkers, opera, Russian literature, and other vast topics of the age, Berlin came to be seen as a giant in 20th-century philosophy, morality, and the history of ideas. A devoted lover of music, Berlin traveled widely to hear particular concerts. He wrote about opera and composers, and had spent time with such musicians as Igor Stravinsky and Alfred Brendel. Berlin also knew many of the towering figures of his age, such as W.H. Auden, Felix Frankfurter, Sigmund Freud, T.S. Eliot, Boris Pasternak, and Jawaharlal Nehru. Berlin spoke half a dozen languages, and in each one, his words spilled out in a torrent.

Berlin was sympathetic to Zionism and felt comfortable in Israel, but his home was clearly in Britain and at Oxford. He was a member and former vice-president of the Oxford Jewish Community, but he was not a religious man. He wrote harshly about communism and fascism as unhealthy totalitarian ideas and delved into problems of free will and liberty in societies founded on those ideas. Many philosophers found his political philosophy and his liberalism to be the most convincing of his day. Berlin also had his detractors. His critics, mainly drawn from the political left, accused Berlin of presenting oversimplified interpretations of political philosophies that conflicted with his defense of traditional liberalism. Others suggested that Berlin's repeated defense of liberalism reflected the type of single-minded worldview that he rebelled against in the works of others.

Berlin died on Nov. 5, 1997, in Oxford. Colleagues and friends remembered him as a humble and warm friend. Many regretted the fact that Berlin refused to write his autobiography, and many were equally amused that Berlin had claimed to have insufficient interest in the subject.