Giuseppe Marco Fieschi was born on 13 December 1790 in Bocognano, a small commune in Corsica. He was the son of Louis Fieschi and Marie Lucie Pomonti, and had two brothers: Thomas, who was later killed during the Battle of Wagram, and Anthony, who was mute from birth. Raised in modest rural conditions, Giuseppe worked as a shepherd in his youth.

At age 18, in 1808, Fieschi enlisted in a Corsican military regiment and was subsequently deployed to Naples and later Russia, serving in the Napoleonic Wars. He rose to the rank of sergeant by 1812. His military service ended with his discharge in 1814, after which he returned to Corsica.

In September 1815, Fieschi joined a failed military expedition led by Joachim Murat, the deposed King of Naples, aimed at reclaiming the Neapolitan throne. The mission collapsed within a month, ending in Murat’s execution. Fieschi escaped execution and was deported to mainland France.

Following his deportation, Fieschi was convicted in 1816 for the theft of a steer and sentenced to 10 years in prison. While incarcerated, he met Laurence Petit, a female inmate with whom he entered into a relationship. After his release in 1826, he moved to Lyon, where Petit was from. During the years that followed, Fieschi relocated to Paris, where he falsely claimed political prisoner status, a tactic that allowed him to move freely and avoid scrutiny.

In Paris, Fieschi engaged in document forgery to secure a minor government post and pensions, which were later revoked upon discovery. His personal life was marked by controversy; he entered into a long-term affair with Nina, his stepdaughter from Laurence Petit, resulting in the deterioration of that relationship. By the early 1830s, Fieschi was jobless, in poor health, and deeply embittered, setting the stage for his involvement in a violent conspiracy.

In 1831, Fieschi met Pierre Morey, a neighbor and former political agitator with Republican sympathies. Morey, then aged 61, had a history of revolutionary activity and legal troubles. The two began plotting a politically motivated assassination using an unconventional weapon—a homemade volley gun, later known as the "infernal machine."

Morey introduced the plan to Théodore Pépin, a radical political figure associated with the Society of the Rights of Man. The trio agreed to fund and build the weapon, which consisted of 25 gun barrels designed to fire simultaneously. Fieschi was tasked with constructing the device in a third-floor apartment at 50 Boulevard du Temple, the exact location where the assassination was to be carried out.

On 28 July 1835, during the annual military review commemorating the July Revolution, King Louis Philippe I passed along Boulevard du Temple with his sons and military entourage. As the procession moved beneath the apartment, Fieschi activated the volley gun. The device discharged approximately 400 projectiles, though not all barrels functioned as intended.

The attack killed 18 individuals either instantly or shortly thereafter, including Marshal Édouard Mortier, several high-ranking military officers, and Alexandre Labrouste, father of architect Henri Labrouste. Twenty-two others were wounded, four of whom required amputations. The King suffered a minor forehead wound, but remained upright and continued with the event. His horse, however, was fatally injured.

Four barrels of the gun exploded, severely injuring Fieschi and damaging the apartment. He suffered head, facial, and hand wounds, and two of his fingers were amputated. Fieschi attempted to flee but was apprehended shortly after. He initially gave a false identity, but his real name was confirmed days later by prison officials.

Fieschi’s trial in early 1836 became a public spectacle. He displayed arrogance, implicated his co-conspirators, and appeared to believe he would be pardoned. He was represented by three lawyers, including the Corsican François-Marie Patorni. The court found him guilty, and he was sentenced to death.

On 19 February 1836, Fieschi was executed by guillotine in Paris alongside Pierre Morey and Théodore Pépin. Pépin and Morey were executed first. Fieschi, the last to die, delivered a speech in his final moments. His head was preserved and given to medical professionals at Bicêtre Hospital for anatomical and psychological study.

Following Pépin’s execution, he made confessions implicating various revolutionary organizations, leading to several arrests. One additional accomplice was sentenced to 20 years in prison, and another was acquitted. Within that year, authorities disrupted seven more plots against King Louis Philippe.

The "infernal machine" used in the assassination attempt was preserved and is now part of the Musée des Archives Nationales in Paris. A commemorative plaque still marks the site at 50 Boulevard du Temple.

Fieschi’s remains became objects of scientific and artistic interest. His death mask was preserved in various collections, including in Norwich Castle and at the University of Edinburgh. A postmortem of his brain was conducted by anatomists Louis Gratiolet and François Leuret in an effort to understand the biological roots of violent behavior.

Though King Louis Philippe survived, the attempt marked a turning point in French political history, prompting tighter security measures and significant repression of dissent in the years that followed.