They were betrothed at a very young age. But when the King was at a marrying age, the princess was still a child. So they sent Princess Mariana back to her native country Spain, and King Louis married Princess Marie Leszczyńska.
After the War of the Quadruple Alliance, France and Spain decided to reconcile by engaging the Infanta Mariana Victoria to her first cousin the young Louis XV of France. Organised by Philippe d'Orléans, Regent of France for the ten year old Louis XV, the match was part of a wider set of engagements which included the proposal of Philip V's eldest son Infante Louis, Prince of Asturias to Élisabeth d'Orléans, Mademoiselle de Montpensier followed by another proposal between Philippine Élisabeth d'Orléans, Mademoiselle de Beaujolais to the young Infante Charles.
In 1721, Louis XV was betrothed to his first cousin, Infanta Maria Anna Victoria of Spain. The eleven-year-old king was not interested in the arrival of his future wife, the three-year-old Spanish Infanta.
Saint-Simon, the French ambassador, requested her hand on 25 November 1721. The exchange of the young Infanta and Mademoiselle de Montpensier was on the Île des Faisans ("Isle of Pheasents") and was the site was where their common ancestors, Louis XIV and Maria Theresa of Austria had met in 1660. Mariana Victoria arrived in Paris on 2 March 1721 amongst much celebration and took up residence at the Palais du Louvre. The young Infanta was nicknamed the l'infante Reine ("Queen-Infanta") as the couple were not to be married till Mariana Victoria reached a more mature age. Mariana Victoria was in awe of Louis XV and was popular with the court apart from the king himself who avoided her presence.
According to the mother of the Régent, Elizabeth Charlotte of the Palatinate, Mariana Victoria was the "sweetest and prettiest little thing" and had considerable wit for her age.
In June 1722, the young king and the court returned to Versailles, where they would stay until the end of the reign. In October of the same year, Louis XV was officially crowned in Reims Cathedral.
Her establishment in France was not to be. Under the influence of the Prime Minister Louis Henri, Duke of Bourbon and his mistress Madame de Prie, the decision was made to send the seven year old Mariana Victoria was sent back to Spain on 11 March 1725.
The Duke of Bourbon was worried by the health of the young king. His primary motivation was a desire to prevent the family of the late regent, the House of Orléans, from ascending the throne should the king die. The duc de Bourbon saw the House of Orléans as his enemy. The king was quite frail, and several alerts led to concern for his life. The Spanish infanta was too young to produce an heir. Thus, the Duke of Bourbon set about choosing a European princess old enough to produce an heir.
Mariana Victoria left Versailles on 5 April 1725.