There was jubilation at the French socialist party's headquarters and a hero's welcome for their leader Francois Hollande on Sunday night as the left gained 50% of the vote.
Socialists were delighted with their victory
It was a humiliation for President Jacques Chirac's centre-right government, one which few on the left dared hope for after their massive defeat in presidential elections two years ago.
On Sunday night, they celebrated the resurrection of the left in France after taking control of almost every French region - as voters delivered a clear message to President Chirac.
That message came in loud and clear at Mr Chirac's UMP headquarters, where party workers looked slightly shell-shocked as they realised the scale of their defeat.
The government gained just 37% of the vote.
UMP supporters looked on expressionless as Prime Minister Jean-Pierre Raffarin went on TV to admit his government had failed to tackle unemployment quickly enough and may have moved too fast on reforms to pensions, welfare benefits and health-care.
"We haven't done enough to bring down unemployment and I am aware of it," he said.
Hollande got a hero's welcome from the left
"The French people made that very clear today. From now on, the government must take more effective action, while ensuring social justice for all."
The president himself was keeping a low profile on Sunday night, but the atmosphere at his party headquarters was subdued to say the least. The celebratory red wine was left almost untouched on the tables.
This week, Mr Chirac must make a difficult choice - whether to use his prime minister as a scapegoat and get rid of him, or keep him on, politically wounded, to implement the rest of Mr Chirac's unpopular reforms.
Analysts in France say the president may well choose to keep Mr Raffarin on, as the alternatives may be no better, or - more dangerous for Mr Chirac - far too popular with the public.
Chirac is said to be considering a reshuffle
One of the most obvious candidates for prime minister is the ambitious and much-liked Interior Minister Nicolas Sarkozy.
The French president may decide that no action is the safest course of action, and put in motion only a limited cabinet reshuffle until after the European elections in June.