In 1940, Hitler invaded Paris; scuffles left a couple of German soldiers wounded outside the Gare du Nord, but otherwise the French acquiesced in gloomy silence. The city's new masters meant business. Any citizen found in possession of firearms would be arrested, or shot.

Agnès Humbert, a middle-aged intellectual in Paris, instinctively felt a moral revulsion for Hitler and the Jew-hatred of Vichy France. The decision to enter the resistance, then, was not difficult for her. While she did not blow up any bridges, derail locomotives or kill members of the SS, she ran extraordinary risks in smuggling anti-Nazi propaganda past German blockades and establishing a network of underground contacts. Humbert's was among the first resistance cells in occupied France and, miraculously, never lost sight of a future beyond Hitler's defeat.

Immediately after the war, in 1946, Humbert published a journal of her five-year struggle against the Nazi regime. It is now translated for the first time in English, and one can only marvel at its 60-year neglect. Despite its often gruesome subject matter (the torture and execution of fellow conspirators), Résistance has flashes of self-deprecating humour, and its affirmation of human dignity instils a kind of joy in the reader. “I suppose the Bible will be classified as subversive because it is non-Aryan!” Humbert comments of Hitler's anti-semitic decrees. The humour was hard-won. In 1942, Humbert was deported as a slave labourer to Germany, where every effort was needed to get to the end of the day alive.

Humbert's survival is not easily explained. Born in Dieppe in 1894, she was 47 when the Gestapo arrested her in 1941, and no longer so resilient. Women generally suffered more grievously under Nazi captivity than men. Starvation left them without breasts or hips; menstruation ceased. Humbert had no soap or change of underwear: the instinct for cleanliness quickly vanished in her. To fellow inmates she was known as “Gandhi” for her emaciated figure; bruises showed blue on her body from the wardens' truncheons; her clothes crawled with lice. Yet her pride and determination not to be crushed provided her with a moral armour and, it seems, a bastion against death.

The journal opens on June 7, 1940 on the eve of the fall of France. Humbert is frantically recording thoughts and events, conversations, things heard and seen on the streets of Paris as occupation looms. The writing here creates an extraordinary sense of communion and intimacy with the reader, as the anti-German underground rapidly gathers momentum in Paris. Humbert was then working at the city's anthropological institute, the Musée de l'Homme - a hotbed of dissent. With a group of fiercely motivated colleagues she decides to scrawl slogans on banknotes and distribute copies of an anti-Nazi journal.

Humbert's nerves are strung out, and at one point she is tempted to give up. However, her courage is galvanised by General de Gaulle, whose patriotic appeals to the French people were broadcast by the BBC that fateful summer of 1940. (“He has given me hope, and nothing in the world can extinguish that hope now.”) With a renewed sense of purpose, Humbert acts as secretary and runner for the Gaullist Free French in France movement, which has made contact with the museum network.

In 1941, however, the network was betrayed to the Gestapo, and in the show trial that followed, seven of the conspirators were executed and three sent to Germany for “war work”. Humbert found herself at a Lager (prison camp) attached to a rayon factory near Düsseldorf. For her 17 months there, she was put on starvation rations and “suffered physical pain in all its manifestations”. Violence was the universal shorthand of the Lager (the language understood by all) and new batches of prisoners were constantly brought in to replace the dead or dying.

After Humbert was liberated by the Americans in April 1945, she began to transpose her impressions of the Lager into a notebook. Memory was all she had to go on for this part of the book - there was no other resource. But her hardest task as she set down her humiliations and torments was to contain her anger. (If she gave way to moral outrage, it might tarnish her credibility as a witness.) The result was a marvel of luminous precision and restraint. Résistance, beautifully translated by Barbara Mellor, is a book of commemoration as well as a documentary: if the Nazi crime cannot be reversed by the writer's pen, at least it can be chronicled. All life is in these burning pages, which bear eloquent witness to the moral and material ruins of Hitler's Germany.

Résistance by Agnès Humbert
Bloomsbury £14.99 pp384

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