Martin Guerre is set in a 16th century French village called Artigat. Pierre Guerre, a wealthy landowner, has arranged that his reluctant young nephew, Martin, should marry Bertrande, the daughter of his very close friend Mme De Rols. The marriage of such two wealthy landowning families, and the prospect of a Catholic heir, ensures the safety of Artigat from the Protestant threat that surrounds them. However, Martin is unhappy as he does not yet feel ready for marriage and having his life planned out for him. Bitter and humiliated he leaves Bertrande and the village to start a new life.

Seven years later, on a battlefield in Flanders, the soldier Martin Guerre tells his friend, the mercenary Arnaud du Thil the story of his childhood and his forced marriage. Arnaud urges Martin to return home but they are suddenly attacked by the ennemy. Shielding Arnaud, Martin is stabbed and is left for dead on the battlefield.

In Artigat, Bertrande is under pressure to remarry and take a new husband. A stranger appears, he is Arnaud du Thil who has come to bring Bertrande news of Martin's death. The village is overjoyed, immediately concluding that he is Martin, returned from the war to at last give his wife and Artigat a Catholic heir. So convinced are they of this, that they prevent Arnaud from contradicting them. Bertrande arrives and, left alone with the newcomer, she soon realizes that his man is not Martin. However, they find themselves drawn to each other, and he agrees to stay in Artigat and keep up the pretence in order to protect her.

Meanwhile Martin Guerre has survived his near fatal injury and is on his way back to Artigat.