Mário de Sá-Carneiro (pronounced [ˈmaɾju ðɨ ˈsa kɐɾˈnɐjɾu]; May 19, 1890 – April 26, 1916) was a Portuguese poet and writer.

Although his father continued to pay for his studies, Sá-Carneiro stopped attending classes very soon after arriving in Paris.

Together with Fernando Pessoa and Almada Negreiros, he wrote for Orpheu, a literary journal of poetry and artistic prose influenced by cosmopolitanism and the European Avant-Garde.

While World War I was in progress in the north of France, he left the university and started a relationship with a prostitute.

In 1910, he wrote his first play, Amizade (the title means friendship), in partnership with Tomás Cabreira Júnior.

On the 9th of January 1911, Tomás Cabreira Júnior fatally shot himself with a shotgun in the middle of the school's playground, causing Sá-Carneiro to write the poem "A um suicida" (To a suicidal).

He wrote another book, Indícios de Oiro, but it was not published until over twenty years after his death, in the magazine Presença.

His literary influences include Edgar Allan Poe, Oscar Wilde, Charles Baudelaire, Stéphane Mallarmé, Fyodor Dostoevsky, Cesário Verde and António Nobre.