Mariana Victoria of Portugal (or of Braganza; Portuguese: Mariana Vitória; full name: Mariana Vitória Josefa Francisca Xavier de Paula Antonieta Joana Domingas Gabriela de Bragança; Portuguese pronunciation: [mɐɾiˈɐnɐ] or [mɐˈɾiɐ ˈɐnɐ viˈtɔɾiɐ ʒuˈzɛfɐ]; 15 December 1768 – 2 November 1788) was a Portuguese Infanta (princess), the eldest daughter of Queen Maria I of Portugal and her king-consort, Infante Pedro of Portugal.

Mariana Victoria was born at the Royal Palace of Queluz, near Lisbon. She was named after her maternal grandmother, Mariana Victoria of Spain, a daughter of Philip V of Spain.

Her grandmother Mariana went to Spain in 1777 to discuss an alliance with her brother Charles III of Spain. While there, she helped to bring about the marriage of Mariana Victoria and the Spanish king's younger son, Infante Gabriel, her mother's first cousin. They married by proxy on 12 April 1785 at the Ducal Palace of Vila Viçosa. The couple met for the first time at the Royal Palace of Aranjuez on 23 May and had another nuptial ceremony.

The royal couple had three children, of whom two died young. At the birth of her last child, Infante Carlos, she and her husband were in residence at Gabriel's private residence, the Casita del Infante at El Escorial. While there, Gabriel caught smallpox and died at the Casita aged only 36. His wife also succumbed to the illness and died on 2 November; Infante Carlos himself died a week after his mother.

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