Charles Julien Brianchon (19 December 1783 – 29 April 1864) was a French mathematician and chemist.

He entered into the École Polytechnique in 1804 at the age of eighteen^{[dubious – discuss]}, and studied under Monge, graduating first in his class in 1808, after which he took up a career as a lieutenant in Napoleon's artillery. Later, in 1818, Brianchon became a professor in the Artillery School of the Royal Guard at Vincennes.

Brianchon is best known for his proof of Brianchon's theorem (1810).

Brianchon's book Mémoire sur les lignes du second ordre (Paris, 1817) is available online .

• Brianchon's Theorem
• O'Connor, John J.; Robertson, Edmund F., "Charles Julien Brianchon", MacTutor History of Mathematics Archive, University of St Andrews