Projections on Sunday showed the Socialist party crashing to 15-40 MPs in the new national assembly from 277 currently.
As well as being set to lose seats the party has already lost some key figures in parliament as former presidential candidate Benoit Hamon and party boss Jean-Christophe Cambadelis, a 20-year veteran of parliament, lost his seat along with a host of senior figures and former ministers.
Cambadelis said the results were “an unprecedented retreat of the left as a whole and the PS (Socialist Party) in particular.”
In the presidential election, Socialist candidate Benoit Hamon scored a humiliating 6.3 percent in the first round on April 23 after a campaign during which many party heavyweights abandoned him. Perhaps not surprisingly he lost his seat on Sunday.
Others from the outgoing government to suffer the ignomy of a first-round exit included former interior minister Matthias Fekl and ex-culture minister Aurelie Filippetti. Former government minister Cecile Duflot, who is with France's green party also lost her seat.
Several other Socialist figures qualified for the second round but face losing their seats in next Sunday's round including ex-education minister Najat Vallaud-Belkacem and ex-Justice Minister Jean-Jacques Urvoas.
If the projections are confirmed by a second-round of voting next weekend, the collapse would be even worse than in 1993 when the party fell to 56 seats from 278 at the latter end of Socialist president Francois Mitterrand's second
The reasons are multiple, foremost among them the historic unpopularity of Hollande after his five-year term in power which was marked by high unemployment, terror attacks and infighting in the party. At one point, his approval rating hit 4.0 percent.
The left also went into Sunday's elections deeply divided, with the Socialists, the new far-left party France Insoumise (France Unbowed) and the Communist party fielding rival candidates in many constituencies.
Opposite them were new faces from President Emmanuel Macron's centrist party Republique En Marche (Republic on the Move, REM) who have siphoned away centre-left voters.
Julien Dray, a senior Socialist leader, said it was “a profound political crisis. Firstly we'll have to see the second round… we need to keep fighting and afterwards we will need to rework completely what was the Socialist identity.”
The party has gone backwards in every national election since Hollande came to power in 2012, but the presidential election last month and this weekend's parliamentary vote has laid bare the level of disaffection.
“The tornado was too strong… the two elections were too close to allow us to really recover,” Cambadelis added on Sunday.
In the presidential election, Socialist candidate Benoit Hamon scored a humiliating 6.3 percent in the first round on April 23 after a campaign during which many party heavyweights abandoned him. He also lost his seat on Sunday.
Others from the outgoing government to suffer the ignomy of a first-round exit included former interior minister Matthias Fekl and ex-culture minister Aurelie Filippetti.
The party has already raised the possibility of having to sell its headquarters in central Paris as it haemorrhages donations and public subsidies which are essential to keep it afloat.
“The results for the Socialists need to be looked at with clarity and we will need to draw the right conclusions,” former Socialist prime minister Bernard Cazeneuve said in a statement, adding that the party would needed to be “rebuilt on a healthy and renovated basis”.
During Hollande's term, a profound ideological split in the party between traditional leftwingers attached to the power of the state and more pro-market centrists frequently surfaced and remains unresolved.
Projections on Sunday indicated that Macron's centrist party and its allies were on course for a huge majority of 390-445 seats in the 577-member National Assembly.
Macron served as economy minister in the previous Socialist government, but fell out with the party's leaders over his desire to push pro-business and market-friendly reforms.
The 39-year-old was briefly a Socialist party member in his twenties, but started his En Marche movement last April in a bid to redraw French politics around a new centrist force at the expense of traditional parties.