Fortunately, the painting was unharmed in the strange attack.
The identity of the man and motive for the attack are unknown, but as he was escorted from the room he shouted "think about the Earth".
"There are people who are destroying the Earth, think about it," he said in French, according to Twitter users.
"All the artists tell you, think about the Earth, all artists think about the Earth, that's why I did this. Think about the planet."
It's not the first time the Mona Lisa has been attacked. In 2009, a Russian woman threw a ceramic cup at the portrait, reportedly frustrated at having failed to obtain French nationality.
It was the first attack since 1974, when the painting was on display at the Tokyo National Museum and a woman with a disability, so upset by the museum's inaccessibility, attempted to spray red paint on the canvas.
In 1956, the painting was damaged by two attacks: One with acid, and another with a rock – which chipped a speck of pigment from the picture. Those incidents prompted the Louvre to place bulletproof glass around the Mona Lisa.
Indeed, it was a crime that made her legendary when, in August 1911, she was stolen from the walls of the Louvre by Italian handyman Vincenzo Peruggia.
Peruggia was hired by the museum to make protective glass cases for some of its most famous works – including La Gioconda. He hid in a closet at the museum overnight and simply removed the painting from the wall and walked out of the building with the help of an unknowing plumber.
Almost instantly the Mona Lisa became a household name.
After a two-year search, Peruggia was found, arrested and sentenced to seven months in jail – he reportedly thought he would be a national hero for returning the Mona Lisa to Italian soil – and she was restored to the Louvre wall.
Today, the painting is the jewel in the Louvre's crown, attracting millions of visitors each year.
She was created between 1503 and 1519 by Italian Renaissance master Leonardo da Vinci and has become the most famous and most replicated painting in the world, immortalised in everything from fashion to pop art, to novels and films including The Da Vinci Code and Mona Lisa Smile.