She was born in Madrid, the daughter of Prince Antoine, Duke of Montpensier, and Infanta Luisa Fernanda of Spain.

[10] Queen Mercedes co-initiated the building of the Cathedral of la Almudena in Madrid, opposite of the royal palace —the construction beginning in 1883.

A town in the northern Philippine province of Isabela was named Reina Mercedes in her honor in 1886 when the Spanish colonial government formally separated it from Cauayan.

When the King's minister Cánovas del Castillo suggested that he take a new wife, Alfonso acquiesced, choosing Mercedes' sister María Cristina.

[citation needed] In late 1879, he married Archduchess Maria Christina of Austria-Teschen; the eldest of their children, the Princess of Asturias, was named in honour of Queen Mercedes.