Infanta Maria Teresa of Portugal (or of Braganza; Portuguese pronunciation: [mɐˈɾiɐ tɨˈɾezɐ] or [ˈtɾezɐ]; 29 April 1793 – 17 January 1874) was the firstborn child of John VI of Portugal and Carlota Joaquina of Spain, and heir to the throne of Portugal between 1793 and 1795, until her short-lived brother António Pio was born.

Maria Teresa Francisca de Assis Antónia Carlota Joana Josefa Xavier de Paula Micaela Rafaela Isabel Gonzaga was born in Ajuda, Lisbon in 1793. As the eldest child of the heir to the Portuguese monarch, she was granted the title Princess of Beira (given to the son of the heir to the throne). Maria Teresa was the eldest daughter of King John VI of Portugal, then the heir-apparent of the reigning queen Maria I of Portugal, and his wife Carlota Joaquina, daughter of Charles IV of Spain.

She was married on 13 May 1810 in Rio de Janeiro (where the royal family was exiled because of the Napoleonic wars) to her cousin Infante Pedro Carlos, Prince of Spain and Portugal. She was widowed on 26 May 1812, soon after giving birth to her only child, a son, Infante Sebastian of Portugal and Spain (1811–75).

Very conservative, she was an ally of her younger brother Miguel I of Portugal in his attempts to obtain the throne of Portugal (civil war 1826–34), and of her brother-in-law and uncle Infante Don Carlos, Count of Molina in his attempts to obtain the Spanish throne. In the last years of the reign of her uncle Ferdinand VII of Spain (died 1833), Teresa lived in Madrid and plotted to strengthen Don Carlos' position in succession. She participated in the First Carlist War (1833–39), being a leading supporter of Carlism, church and reactionary interests. Her sister Francisca, Titular Queen of Spain, wife of Carlos, died in 1834.

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