He became a member of the National Assembly for LFI following the 2017 French legislative election, receiving 59.9% in the second round in the 4th constituency of Bouches-du-Rhône, located in Marseille (France's second-largest city).

After this, he led the newly formed New Ecological and Social People's Union (NUPES) alliance of parties to a second-place performance in the 2022 French legislative election.

[3] He was originally a follower of Pierre Lambert and a member of the Trotskyist movement before supporting François Mitterrand and joining the Socialist Party (PS).

[11] At the Reims Congress in September 2008, the political current Trait d'union, created after the victory of the "No" in the 2005 French European Constitution referendum, Mélenchon made a new contribution.

[12] For the first time, this motion brought together all the sensibilities of the left wing of the PS, with emblematic personalities like Gérard Filoche, Marie-Noëlle Lienemann, and Paul Quilès.

[14] Believing themselves too far from this trend to the point that it would not be useful to take part in the congress, Mélenchon, alongside Marc Dolez,[15][16] announced on 7 November their decision, "out of fidelity to their commitments", and for their independence of action, to leave the PS, and to create a new movement "without concession facing the right".

[21][22] He took fourth place and achieved 11.10% of the vote, trailing behind François Hollande, Nicolas Sarkozy, and Marine Le Pen and their respective parties (the PS, the Union for a Popular Movement, and the National Front).

During an interview on the French television channel TF1 on 10 February 2016, Melenchon launched the left-wing political platform La France Insoumise,[25][nb 2] without any expectation of victory.

[31] According to political scientist Christopher Bickerton, La France Insoumise was comparable to Podemos in Spain, and Le Baron Noir character Michel Vidal is based on Mélenchon.

[32] According to Bickerton, La France Insoumise is "a flexible organisation, in tune with the individualism of the present", with "no membership as such" and much of its activism being "self-financed and self-organised", and where "Mélenchon gives his approval to initiatives after the fact rather than issuing orders or instructions.

"[34] Mélenchon, who saw himself as "outside the frame of political parties",[35] held at a consistent 12% for most of the campaign, until a late upwards surge which put him just behind third place François Fillon at 18%.

[40] In June 2017, Mélenchon became a member of the National Assembly for La France Insoumise following his win in the legislative election in the 4th constituency of Bouches-du-Rhône, which covers parts of the centre of Marseille.

[nb 3] The collapse of the Socialist Party meant that La France Insoumise had become the de facto opposition to Emmanuel Macron in the National Assembly.

[43] In December 2019, Mélenchon received a suspended prison sentence of three months for rebellion and provocation following an altercation with police officers who had come to serve a warrant at the La France Insoumise headquarters in Paris.

This dynamic flipped in the 2022 French legislative election as Mélenchon and La France Insoumise had become part of the New Ecological and Social People's Union (NUPES), a broad anti-neoliberal coalition.

[49] According to political scientist Christopher Bickerton, observers commented that "the LFI's electoral offer was the most sophisticated of all the parties — a total of 694 proposals, from a sixth republic to 'rational' anti-terrorist legislation, to a commitment to the demilitarisation of space.

[59] Historian Sudhir Hazareesingh described Mélenchon as a "democratic socialist candidate [who] symbolises France's hunger for social, political, and environmental reform, as well as the popular frustration with the nation’s established elites", and as "a middle-class champion of the working people, a former senator turned radical reformer, a transformative visionary driven by memories of past glories, a digital geek steeped in classical learning, an inveterate critic of presidentialism who is himself a charismatic leader, and a 70-year-old veteran who counts the young among his primary constituencies".

[63] According to political scientist Christopher Bickerton, among the reasons for "Mélenchon's high score in the 2022 presidential election was that he supplemented his earlier populism with an extensive and comprehensive legislative programme.

[nb 6] According to the Belgian public media RTBF, his radical appearance is linked to his criticism of neoliberalism, international treaties, and the functioning of the European Union (EU), as well as his tax reform.

Mélenchon does not support Marxist ideas of "proletarian revolution", as is the case with the New Anticapitalist Party and Lutte Ouvrière, and his tax reform is more moderate than that of the far-left.

"[101] Hazareesingh argued that Mélenchon "mobilised support in deprived inner-city areas, and was the only major candidate who unambiguously denounced racism and Islamophobia, and defended a multicultural vision of Frenchness which, borrowing from the poet Édouard Glissant, he labelled 'créolisation'.

[103] During his 2012 campaign, Mélenchon positioned himself against the trend towards economic globalisation, which he denounced as disproportionately profiting the financial industry and "high income earners" at the expense of the poor.

"[112] Mélenchon has himself his vision of populism, which he sees as positive if it comes with left-wing politics, and believes it is possible to bring about a "citizens' revolution" to usher in "the epoch of the people".

This theory argues that neoliberalism and austerity only made the far-right stronger and that the populist concept of "the people" has to be reintroduced into the political sphere in a civic sense rather than an ethnic way (creating a "right populism" to fight).

[136] Cécile Vaissié, author of The Kremlin Networks, considers Mélenchon as "one of those that approve of Putin",[137] and Yannick Jadot of EELV said that the "pro-Russia" stance is "contrary to any environment thinking".

"[140] Mélenchon declared opposition to Putin's domestic policy and notes his friend of the Russian Left Front, Sergey Udaltsov, is imprisoned in Russia.

[156] Following the 2020 Baghdad International Airport airstrike that resulted in the killing of major general Qasem Soleimani, Mélenchon tweeted: "We must equally condemn the USA and Iran as warmongers.

[185] In November 2019, Mélenchon further accused CRIF of practising "blatant, violent, and aggressive sectarianism, namely against me", after it asked him not to attend the memorial ceremony for Knoll more than 18 months earlier.

[189] In October 2021, Mélenchon was again accused of antisemitism, after he claimed Jewish tradition was opposed to assimilation, and that far-right Éric Zemmour's position on immigration was rooted in this opposition.

[192] In June 2021, Mélenchon predicted that, in the last week of the 2022 presidential campaign, there would be a "grave incident or murder" that would be used to "point the finger at the Muslims and to invent a civil war".