St Bertille was born of one of the most illustrious families in the territory of Soissons, in the reign of Dagobert I, and by her piety acquired the true nobility of the children of God. From her infancy she preferred the love of God to that of creatures, shunned as much as possible the company and amusements of the world, and employed her time in serious duties and chiefly in holy prayer. As she grew up, by relishing daily more and more the sweetness of conversing with God, she learned perfectly to despise the world and earnestly desired to renounce it. Not daring to discover this inclination to her parents, she first opened herself to St. Ouen, by whom she was encouraged in her resolution. Self-love early disguises itself in every shape, and the devil often transforms himself into an angel of light. Not to be deceived through precipitation and rashness in so important a choice as that of a state of life, impartial advice, prayer, careful self-examination and mature deliberation are necessary. These means having been employed, the saint's parents were made acquainted with her desire, which God inclined them not to oppose. They conducted her to Jouarre, great monastery in Brie, four leagues from Meaux, founded not long before, about the year 630, by Ado, the elder brother of St. Ouen, who took the monastic habit there with many other young noblemen and established a nunnery in the neighbourhood, which became the principal house. St. Thelchildes, a virgin of noble descent, who seems to have been educated or first professed in the monastery of Faremoutier, was the first abbess of Jouarre, and governed that house till about the year 660. By her and her religious community St. Bertille was received with great joy and trained up in the strictest practice of monastic perfection. Our saint, looking upon this solitude as a secure harbour, never ceased to return thanks to God for his infinite mercy in having drawn her out of the tempestuous ocean of the world: but was persuaded she could never deserve to become the spouse of Jesus Christ unless she endeavoured to follow him in the path of humiliation and self-denial. By her perfect submission to all her sisters she seemed everyone's servant, and in her whole conduct was a model of humility, obedience, regularity, and devotion. Though she was yet young, her prudence and virtue appeared consummate, and the care of entertaining strangers, of the sick, and of the children that were educated in the monastery was successfully committed to her. In all these employments she had acquitted herself with great charity and edification when she was chosen prioress to assist the abbess in her administration. In this office her tender devotion, her habitual sense of the divine presence, and her other virtues shone forth with new lustre, and had a wonderful influence in the direction of the whole community.
When St. Bathildes, wife of Clovis II, munificently refounded the abbey of Chelles, which St. Clotildis had instituted near the Marne, four leagues from Paris, she desired St. Thelchildes to furnish this new community with a small colony of the most experienced and virtuous nuns of Jouarre, who might direct the novices in the rule of monastic perfection. Bertille was sent at the head of this holy company, and was appointed the first abbess of Chelles, in 646, or thereabouts. The reputation of the sanctity and prudence of our saint, and the excellent discipline which she established in this house, drew several foreign princesses thither. Among others Bede mentions Hereswith, Queen of the East-Angles. She was daughter of Hereic, brother or brother-in-law to St. Edwin, King of Northumberland, and married the religious King Annas, with whose consent she renounced the world and, passing into France, in 646, became a nun at Chelles. Queen Bathildes, after the death of her husband in 655, was left regent of the kingdom during the minority of her son Clotaire III, but as soon as he was of age to govern, in 665, she retired hither, took the religious habit from the hands of St. Bertille, obeyed her as if she had been the last sister in the house, and passed to the glory of the angels in 680. In this numerous family of holy queens, princesses, and virgins, no contests arose but those of humility and charity. The holy abbess, who saw two great queens every day at her feet, seemed the most humble and the most fervent among her sisters, and showed by her conduct that no one commands well or with safety who has not first learned, and is not always reader, to obey well.
St. Bertille governed this great monastery for the space of forty-six years with equal vigour and discretion. In her old age, far from abating her fervour, she strove daily to redouble it both in her penances and in her devotions. In these holy dispositions of fervour the saint closed her penitential life in 692.