The letter dated June 30, 1845, and it was addressed to his lover at the time, Jeanne Duval.
Later that day the poet, who was 24 years old at the time, tried to kill himself but he survived.
According to the French website Osenat, the letter was sold to a private buyer for three times the estimated price.
In the text, Baudelaire tells Duval of his intention to take his own life and says that by the time she reads it "I will be dead."
He said he could "no longer live, or bear the burden of falling asleep and waking up again."
Baudelaire, who led a tortured personal life, lived another 22 years during which he wrote the work that would establish his reputation, Les Fleurs du Mal (The Flowers of Evil).
The poet eventually died from syphilis in 1867.