Marcos António da Fonseca Portugal (March 24, 1762 – February 17, 1830) was a Portuguese classical composer, who achieved great international fame for his operas in Italian.

Portugal was born in Lisbon. He first studied music at the Patriarchal Seminary in Lisbon where, as a 14 year old student, he wrote his first work, a Miserere. He later worked as composer and organist at the Patriarchal See, and was maestro at the Theatre of Salitre in Lisbon. He lived in Italy from late 1792 to 1800, possibly funded by the Prince Regent, D. João. He wrote 21 operas for various Italian theatres, the first being I due gobbi, premièred in Florence in the spring of 1793. His version of The Marriage of Figaro premièred in Venice in 1799.

Marcos Portugal returned to his home country in 1800. The huge success that his opere buffe had earned him assured him a still unsurpassed international fame in Portugal's music history. He became maestro at the Teatro Nacional de São Carlos in Lisbon, and was appointed music master at the Patriarchal Seminary in Lisbon. He continued to write operas, mainly opere serie, and a large number of religious works, until moving to Brazil in 1811, from where the Prince Regent had called him. Upon arriving, Marcos Portugal was appointed music master to the sons and daughters of the Prince Regent, and became the official Royal Composer.

He wrote mainly religious music until at least 1824, date of his last known surviving autograph. In Portugal and Brazil, his reputation rests mainly on his religious music output, a genre cultivated throughout his composing life. He remained in Rio de Janeiro when the Portuguese Court returned to Portugal, in 1821, continuing to serve his pupil, the First Emperor of Brazil, D. Pedro, as he had previously served his father, king John VI of Portugal. He died in Rio de Janeiro in 1830.

In 2010, Bampton Classical Opera presented the UK première of Portugal's The Marriage of Figaro (1799). Marcos Portugal was born six years after Mozart, who had composed his version of Figaro thirteen years prior to Portugal's. Like most theatre composers of the time, Portugal set several librettos that had proven successful for earlier operas, such as Metastasio’s Demofoonte (premièred at La Scala, Milan, in 1794) and Artaserse; and he set many stories that had been used before, including Serse, Alceste, Adrasto, Semiramide and Sofonisba. By reusing earlier librettos and stories, composers could expect their audience to follow the story more easily, which is probably why Portugal decided to do his own version of the famous play by Beaumarchais. His librettist was Gaetano Rossi.