Madame de Rênal is the wife of the mayor of Verrières, in whose house Julien Sorel enters as tutor to the children. She is his first love and, as he himself discovers in prison, the true one.
A rich heiress of a devout aunt, married at sixteen, she "had never in her life felt or seen anything that even remotely resembled love." Her confessor, Abbé Chélan, had spoken to her of love only as libertinism. That is why she falls in love without noticing: she almost loses the reason for her happiness when Julien refuses to marry the maid Élisa, and, hand in hand with him under the linden tree, "she was not thinking of anything, she let herself live."
Her son Stanislas's illness turns love into remorse, and the scandal that follows an anonymous letter drives Julien away from Verrières. Later, when the Marquis de La Mole asks for information about him, she copies a letter written by the young priest who directs her conscience, which accuses Julien of hypocrisy and undoes his marriage. Julien shoots at her in the church. She survives, writes to each of the thirty-six jurors, and goes to the prison to beg him to appeal.
In the novel she works as a yardstick: she is the character who does not calculate, and everything Julien does gains meaning in relation to her. In the last paragraph of the book she keeps the promise made to Julien not to attempt her own life, but three days later she dies embracing her children.