Elisabeth was born in Paris to a wealthy bourgeois French family of Corsican descent. She met Félix Leseur (1861–1950), also from an affluent, Catholic family in 1887. Shortly before they married on July 31, 1889, Elisabeth discovered that Félix was no longer a practicing Catholic.

Though he continued to practice medicine, Dr. Félix Leseur and soon became well known as the editor of an anti-clerical, atheistic newspaper in Paris. Despite his pledge to respect Elisabeth's religious beliefs, as his hatred of the Catholic faith grew he soon began to question, undermine, and ridicule Elisabeth's faith.

In his memoirs, Félix describes how his efforts to "enlighten" Elisabeth nearly succeeded. He had persuaded Elisabeth to read Ernest Renan's Life of Jesus with the expectation that it would finally shatter her last remaining loyalties to Catholicism. Instead, he records that she was "struck by the poverty of substance" on which the arguments were based and was inspired to devote herself to her own religious education.

Soon, their home was filled with two libraries. One, a library devoted to the justifications of atheism and the second to the lives of the saints and the intellectual arguments in favor of Christ and Catholic Church. Félix was frustrated to discover that his challenges to her faith had actually led her to become not only more grounded in her beliefs, but more fervent and determined to become holy.

The couple's religious differences became a burden on their relationship, especially for Elisabeth, who wrote in her journal of the "bitter suffering" she experienced at "hearing my faith and spiritual things mocked at, attacked and criticized" by her husband and their friends during their many evening gatherings. In addition to this strain, they were burdened with the inability to have children and Elisabeth was plagued with a constant battle of physical illnesses. As made explicit in her diaries, Elisabeth endured all of these sufferings with a firm conviction that "suffering is the highest form of action, the highest expression of the wonderful Communion of Saints, and that in suffering one is sure not to make mistakes (as in action, sometimes) ... sure to be useful to others and to the great causes that one longs to serve."

Two years before her death, Elisabeth and Felix were conversing about what each would do after the other had died, and at this point she insisted that "I am absolutely certain that when you return to God, you will not stop on the way because you never do things by halves.... You will some day become a priest." To this he responded: "Elizabeth, you know my sentiments. I've sworn hatred of God, I shall live in the hatred and I shall die in it."

During the last two years of her life, as she was dying of breast cancer, Félix could not help but be impressed by the depth of strength she drew from her spirituality: "When I saw how ill she was, and how she endured with equanimity of temper a complaint that generally provokes much hypochondria, impatience and ill-humor, I was struck to see how her soul had so great a command of itself and of her body; and knowing that she drew this tremendous strength from her convictions, I ceased to attack them."

Following her death from cancer in 1914, Félix discovered in her papers a note directed to him: "In 1905, I asked almighty God to send me sufficient sufferings to purchase your soul. On the day that I die, the price will have been paid. Greater love than this no woman has than she who lay down her life for her husband."

Dr. Leseur dismissed this as the fancies of a pious woman. Nonetheless, he was also amazed to discover that Elisabeth's spiritual efforts had included a huge number of correspondences with people from all walks of life of which he had previously been unaware. During her last few days, many of these unknown people had come to visit and a much larger throng had attended her wake prior to the funeral. So many that Félix was asked by one priest "who was this woman? We have never seen such a funeral before."

Following the funeral, Félix decided to write a book against the miracles of Lourdes. Instead, when visiting Lourdes and looking upon a statue of Mary and reflecting on the "celestial beauty" of his wife's soul he realized that "she had accepted her suffering and offered it...chiefly for my conversion." In perceiving her life as an icon of Christ, who also suffered for his personal salvation, Felix's confidence in atheism crumbled. He returned to the Catholic faith he had been taught as a child and began to diligently study his wife's spiritual writings, which she had begun in 1899 until her death.

Félix subsequently published his wife's journal, and in fall of 1919 became a Dominican novice. He was ordained in 1923 and spent much of his remaining twenty seven years publicly speaking about his wife's spiritual writings. He was instrumental in opening the cause for Elisabeth's beatification as a saint.

In reflecting on his wife's life, Félix recalled that she once wrote a book of her younger sister the epigram "Every soul that uplifts itself uplifts the world." Commenting on this, Félix added, "In that profound thought she defined herself."

In the year 1924, Fulton J. Sheen, who would later become an arch-bishop and popular American television and radio figure, made a retreat under the direction of Fr. Leseur. During many hours of spiritual direction, Sheen learned of the life of Elisabeth and the conversion of Félix. Sheen subsequently repeated this conversion story in many of his presentations, in particular in regard to the role that spouses play in the sanctification of each other.

In commenting on the life of Elisabeth Leseur, Dr. Robin Mass says, "This was a life that completely changed another life ... perhaps many lives ... because it was willing to open itself fully to the possibility that in her and through her own pain and loss, God could do the loving."