Galois' fatal duel took place on 30 May. The true motives behind the duel are obscure. There has been much speculation as to the reasons behind it. What is known is that five days before his death, he wrote a letter to Chevalier which clearly alludes to a broken love affair.[3]
Some archival investigation on the original letters suggests that the woman of romantic interest was a Mademoiselle Stéphanie-Félicie Poterin du Motel,[12] the daughter of the physician at the hostel where Galois stayed during the last months of his life. Fragments of letters from her, copied by Galois himself (with many portions, such as her name, either obliterated or deliberately omitted), are available.[13] The letters hint that Mlle. du Motel had confided some of her troubles to Galois, and this might have prompted him to provoke the duel himself on her behalf. This conjecture is also supported by other letters Galois later wrote to his friends the night before he died. Galois' cousin, Gabriel Demante, when asked if he knew the cause of the duel, mentioned that Galois "found himself in the presence of a supposed uncle and a supposed fiancé, each of whom provoked the duel." Galois himself famously exclaimed: "I am the victim of an infamous coquette and her two dupes."[7]
Much more detailed speculation based on these scant historical details has been interpolated by many of Galois' biographers (most notably by Eric Temple Bell in Men of Mathematics), such as the frequently repeated speculation that the entire incident was stage-managed by the police and royalist factions to eliminate a political enemy.[9]
As to his opponent in the duel, Alexandre Dumas names Pescheux d'Herbinville,[8] who was actually one of the nineteen artillery officers whose acquittal was celebrated at the banquet that occasioned Galois' first arrest.[14] However, Dumas is alone in this assertion, and if he were correct it is unclear why d'Herbinville would have been involved. It has been speculated that he might have been du Motel's "supposed fiancé" at the time (she ultimately married someone else), but no clear evidence has been found supporting this conjecture. On the other hand, extant newspaper clippings from only a few days after the duel give a description of his opponent (identified by the initials "L.D.") that appear to more accurately apply to one of Galois' Republican friends, most probably Ernest Duchatelet, who was imprisoned with Galois on the same charges.[15] Given the conflicting information available, the true identity of his killer may well be lost to history.
Whatever the reasons behind the duel, Galois was so convinced of his impending death that he stayed up all night writing letters to his Republican friends and composing what would become his mathematical testament, the famous letter to Auguste Chevalier outlining his ideas, and three attached manuscripts.[16] Mathematician Hermann Weyl said of this testament, "This letter, if judged by the novelty and profundity of ideas it contains, is perhaps the most substantial piece of writing in the whole literature of mankind." However, the legend of Galois pouring his mathematical thoughts onto paper the night before he died seems to have been exaggerated.[3] In these final papers, he outlined the rough edges of some work he had been doing in analysis and annotated a copy of the manuscript submitted to the Academy and other papers.

The Galois memorial in the cemetery of Bourg-la-Reine. évariste Galois was buried in a common grave and the exact location is still unknown.
Early in the morning of 30 May 1832, he was shot in the abdomen, abandoned by his opponents and seconds, and was found by a passing farmer. He expired the following morning at ten o'clock in the Cochin hospital (probably of peritonitis), after refusing the offices of a priest. There were plans to initiate an uprising during his funeral, but during the same time frame the leaders heard of General Jean Maximilien Lamarque's death, and the rising was postponed without any uprising occurring until 5 June. Only Galois' younger brother was notified of the events prior to Galois' death.[17] He was 20 years old. His last words to his younger brother Alfred were:
“Ne pleure pas, Alfred ! J'ai besoin de tout mon courage pour mourir à vingt ans !”
(Don't cry, Alfred! I need all my courage to die at twenty.)