After the coronation of Philip V as King of Spain and the imminent outbreak of war caused by Charles II’s succession, both the French and the Spanish Monarchy entered into different diplomatic alliances in order to neutralize claims from the Viennese branch of the House of Austria to the Spanish crown. The Italian Peninsula, where France and the Spanish Monarchy had the support of the duchies of Mantua and Savoy, was an important scenario for Bourbon diplomacy. This article aims to analyse the role played by the marriage of Philip V and Mary Louise of Savoy in the signing of the Bourbon-Savoyard Treaty, in April 1701. Based on diplomatic sources located in Spanish, French and Italian archives, this paper focuses not only on the characteristics of the agreement signed between the two dynasties, but also on how the negotiations for the King’s marriage were influenced by the fragility of a politically asymmetric alliance which would break apart just two years after its formalization.