Facundo Machaín (November 26, 1845 – October 29, 1877) was president of Paraguay. His period of government lasted barely one day between August 31 and September 1, 1870, but was important for the political situation and development of the country at the time.

Facundo Machaín Recalde was a lawyer and politician. He was born in Asunción on November 26, 1845. His parents were José Serapio Machaín y Zavala and Clara Recalde y Machaín. He had several siblings: Esteban, León, Raymundo (who later married his widow), Josefa (married Federico Zorraquín), Francisca (married Alberto Robinson), Emilia and Serapio Machaín. He was married to Clara Recalde, but had no children.

After attending school in Asuncion he studied in Chiles Universidad Central where he graduated from Law School. His professor was the Argentine Andrés Bello.

At the end of Paraguayan War in early 1869 he returned to the recently occupied Asuncion and got involved in politics. He quickly became president of the political Gran Club del Pueblo and was elected to the National Assembly. Facundo was one of the first Paraguayan politicians who spoke in public to the people and managed to captivate the audience with his strong personality, his youth and culture. According to the biography written by José Segundo Decoud, Facundo was a good speaker but had difficulties with writing. As a lawyer he was a member of the commission that created the Constitution of 1870.

He worked as a journalist and was professor and the first director of the Colegio Nacional de Asunción (Asunción's National School). From that building he saw the assassination of President Juan Bautista Gill in April 1877. When hearing the first shots he went out to one of the balconies that opened to the Libertad Street (nowadays called Eligio Ayala) shouting: "The President is being killed".

He agreed to defend those accused for the murder of President Gill. However, the political situation made him a victim of political passions. He was imprisoned and placed in the same cell as his defendants, among whom was José Dolores Molas, an army officer who a few years earlier had led a revolt against the government in Asuncion.

Under orders from Candido Bareiro and Bernardino Caballero, Facundo was murdered by prison guards in his prison cell on 29 October 1877 at the age of 32. His death caused great sadness in Paraguayan society. It was said that with him Paraguayan writing lost a great professor.

A street in Asuncion, in the neighborhood of Mariscal Estigarribia is named in his honor.