In an interview a few weeks before his death Judt said: "I see myself as first and above all a teacher of history; next a writer of European history; next a commentator on European affairs; next a public intellectual voice within the American Left; and only then an occasional, opportunistic participant in the pained American discussion of the Jewish matter…"

Born in 1948 in London, England, Judt was raised in South London by a mother whose parents had emigrated from the Russian Empire and a father who was born in Belgium and had emigrated as a boy to Ireland and then England. Judt was educated at Emanuel School, a Christian grammar school in Wandsworth, south-west London, before going on to study as a scholarship student at King's College, Cambridge. Judt was the first member of his family to finish secondary school and to go to university. He obtained a BA degree in history in 1969 and, after spending a year at the École Normale Supérieure in Paris, completed a PhD in 1972. As a high school and university student he was a left-wing Zionist, and worked summers on kibbutzim. He moved away from Zionism after the Six-Day War of 1967, but remained impressed by Marxism as a tool of analysis.

After completing his Cambridge doctorate, he was elected a junior fellow of King's College in 1972, where he taught modern French history until 1978. Following a brief period teaching social history at the University of California, he returned to Great Britain in 1980 to teach politics at Oxford University. He moved to New York University in 1987.

Judt was married three times, with his first two marriages ending in divorce. His third marriage was to Jennifer Homans, The New Republic's dance critic, with whom he had two children. In a review of Judt's Reappraisals: Reflections on the Forgotten Twentieth Century, Jonathan Freedland writes that Judt has put conscience ahead of friendship during his life, and has demanded the same courage in others.

Judt's experiences in Paris contributed to what would become a long and fruitful relationship with French political culture. He translated his Cambridge doctorate into French and published it in 1976 as La reconstruction du parti socialiste: 1921-1926. It was introduced by Annie Kriegel, who along with Maurice Agulhon was an important influence upon his early work as a French social historian. Judt's second book, Socialism in Provence 1871-1914: A Study in the Origins of the French Modern Left, an “enquiry into a political tradition that shaped a nation”, was an attempt to explain early origins and the continuities of left-wing politics in the region. More than any other work by Judt, Socialism in Province was based upon extensive archival research. It was his one and only attempt to place himself within the social history that was dominant in the 1970s.

In the 1970s and 1980s Judt was a historian of modern France. Marxism and the French Left: Studies in Labour and Politics in France 1830-1981 collects several previously unpublished essays on the nineteenth and twentieth centuries, ending with a discussion of Mitterand. In Past Imperfect: French Intellectuals, 1944-1956, Judt moved away both from social history towards intellectual history, and from endorsement of French Marxist traditions to their critique. In Past Imperfect, he castigates French intellectuals of the postwar era, above all Jean-Paul Sartre for their “self-imposed moral amnesia.” Judt has criticized what he considered blind faith in Stalin’s communism. In Judt's reading, French thinkers such as Jean-Paul Sartre were blinded by their own provincialism, and unable to see that their calls for intellectual authenticity should have required them to interrogate their own attachment to communism and criticize the Soviet Union for its policies in postwar eastern Europe. This was in some sense a criticism from within, using French sources and polemical style against famous French intellectuals. Judt made a similar case in some of his more popular writings. For instance, following the recognition by then President Jacques Chirac, in 1995, of the responsibility of the French state during the Collaboration, on the anniversary of the Vel' d'Hiv raid, he claimed in an op-ed published by The New York Times that:

"people like Jean-Paul Sartre and Michel Foucault were curiously silent. One reason was their near-obsession with Communism. While proclaiming the need to "engage," to take a stand, two generations of intellectuals avoided any ethical issue that could not advance or, in some cases, retard the Marxist cause. Vichy was dismissed as the work of a few senile Fascists. No one looked closely at what had happened during the Occupation, perhaps because very few intellectuals of any political stripe could claim to have had a "good" war, as Albert Camus did. No one stood up to cry "J'accuse!" at high functionaries, as Emile Zola did during the Dreyfus affair. When Simone de Beauvoir, Roland Barthes and Jacques Derrida entered the public arena, it usually involved a crisis far away -- in Madagascar, Vietnam or Cambodia. Even today, politically engaged writers call for action in Bosnia but intervene only sporadically in debates about the French past."

In the years following the publication of Past Imperfect, Judt turned his attention to the wider issues of European history. He spent the 1980s and much of the 1990s at Emory, Oxford, Stanford, and Vienna, where he taught political theory, learned Czech, and became friendly with a number of east European intellectuals. Erich Maria Remarque’s widow, actress Paulette Goddard, bequeathed her fortune to NYU and thus the Institute of European Studies bearing her late husband’s name came into being under Judt’s direction. Judt's first broader book of this period – the result of a speech delivered at the Johns Hopkins-SAIS Bologna Center in 1995 – was A Grand Illusion? In this extended essay, he dealt directly with the European Union and its prospects for the future, which, in his view, were quite bleak. According to Judt, Europe’s sense of its divisions had long been one of the “defining obsessions of its inhabitants."

The benefits of unity were unevenly distributed and the regions it favored came to have more in common with each other than with their neighbors living in the same state. The Baden-Württemberg region in southwestern Germany, the Rhône-Alpes region of France, Lombardy and Catalonia are evoked as examples of disproportionately rich “super-regions.” Another division, Judt claims, could be seen in the Schengen Agreement. Nothing more than a “highest common factor of discriminatory political arithmetic,” the Schengen Agreement made Eastern European countries into barrier states designed to keep undesirable immigrants at bay. Similar dangers existed in eastern Europe where former critics of Soviet universalism deftly recycled themselves into anti-European, nationalist agitators.

These problems, Judt writes, could find their resolution only in increased national intervention. States would be called upon to redistribute wealth and preserve the decaying social fabric of the societies they governed. This conception of the role of the state is carried over – albeit in slightly different form - into Judt's 2005 book, Postwar: A History of Europe Since 1945.