| Benjamin Constant | |
| Office: | Minister of War |
| Term Start: | 15 November 1889 |
| Term End: | 12 March 1890 |
| President: | Deodoro da Fonseca |
| Predecessor: | Viscount of Maracaju |
| Successor: | Eduardo Wandenkolk |
| Office2: | Secretary of State of Public Instruction, Posts and Telegraphs |
| Term Start2: | 19 April 1890 |
| Term End2: | 21 January 1891 |
| President2: | Deodoro da Fonseca |
| Predecessor2: | Office established |
| Successor2: | João Barbalho (interim) |
| Birth Date: | 18 October 1836 |
| Birth Place: | Niterói, Rio de Janeiro, Empire of Brazil |
| Death Place: | Rio de Janeiro, Neutral Municipality, Brazil |
| Party: | Republican |
| Children: | 8 |
| Father: | Leopoldo Henrique Botelho de Magalhães |
| Mother: | Bernardina Joaquina da Silva Guimarães |
| Education: | Praia Vermelha Military School |
| Allegiance: | Empire of Brazil (until 1889) United States of Brazil |
| Branch: | Imperial Brazilian Army Brazilian Army |
| Serviceyears: | 1852-1891 |
| Rank: | Lieutenant colonel |
| Battles: | Paraguayan War |
Benjamin Constant Botelho de Magalhães (18 October 1836 – 22 January 1891) was a Brazilian military officer and political thinker. Primarily a positivist, influenced heavily by Auguste Comte, he was the founder of the positivist movement in Brazil (Sociedade Positivista do Brasil, Brazilian Positivist Society), and later this led to his republican views. He left the Brazilian Positivist Society because of internal disagreements, but remained an ardent pupil of Comte until the end of his life.
Benjamin Constant was born in Niterói. He had a difficult childhood and attempted suicide at the age of 12. He served in the Paraguayan War, and had a large family. He felt underpaid and unhappy as a soldier. An intellectual at heart, he was a great supporter of Comte's Religion of Humanity.
His republican views led him to found the Clube Militar (or Military Club), with Deodoro da Fonseca, in May 1887.[1] It was based in the Praia Vermelha Military School, and, shortly before his death, helped to organize a coup to overthrew Emperor Pedro II and establish a republic.
The Brazilian town of Benjamin Constant, Amazonas, near the Amazon River and the Peruvian border, was named after him.
He was considered the founder of the Republic in the Constitution of 1891, having died earlier the same year in Rio de Janeiro, aged 54.