Claude was born on 13 October 1499 in Romorantin-Lanthenay[1] as the eldest daughter of King Louis XII of France and his second wife, Duchess Anne of Brittany.

Eager to keep Brittany separated from the French crown, Queen Anne, with help of Cardinal Georges d'Amboise, promoted a solution for this problem, a marriage contract between Claude and the future Holy Roman Emperor Charles V.[3] This sparked a dispute between the Cardinal and Pierre de Rohan-Gié [fr] (1451–1513), Lord of Rohan, known as the Marshal of Gié, who fervently supported the idea of a marriage between the princess and Francis, Duke of Valois, the heir presumptive to the French throne, which would keep Brittany united to France.

A part of the contract promised the inheritance of Brittany to the young prince, already the next in line to thrones of Castile and Aragon, Austria and the Burgundian Estates.

[5] In 1505, her father, Louis, very sick, cancelled Claude's engagement to Charles in the Estates Generals of Tours, in favor of his heir, Francis, Duke of Valois.

With this union, it was secured that Brittany would remain united to the French crown, unless the third marriage of Louis with Mary of England (celebrated on 9 October 1514) produced the long-waited heir.

Unlike her younger sister Renée, she seems to have never showed any interest in her maternal inheritance nor had any disposition to politics, as she preferred to devote herself to religion under the influence, according to some sources, of Christopher Numar of Forlì, who was the confessor of her mother-in-law.

Gabriel Miron repeated his functions under Anne of Brittany and remained as chancellor of Queen Claude and first doctor; he wrote a book entitled de Regimine infantium tractatus tres.

[13]The pawn of so much dynastic maneuvering, Claude was short in stature and affected by scoliosis, which gave her a hunched back, while her husband was bigger and athletic.

Foreign ambassadors noted her "corpulence", claudication (tendency to limping), the strabismus affecting her left eye, her small size, and her ugliness, but they acknowledged her good qualities.

Foreign ambassadors noted her "strong corpulence", her limp, the strabismus of her left eye, her short stature, her ugliness, and her reserve, but they also emphasized her good-hearted nature.