French President Nicolas Sarkozy’s conservative government has lost its majority in the Senate for the first time in recent French history.
The Socialist Party and its Communist and Green allies have won enough seats to gain control of the upper house.
Their victory comes just seven months before the country’s presidential election in April.
Right-wing parties have controlled the Senate since the Fifth Republic was founded in 1958.
Early results from the indirect elections showed left-wing candidates took at least 23 seats from the governing conservative party, giving them an absolute majority.
“The 25th of September, 2011, will go down in history,” Jean-Pierre Bel, head of the Socialist group in the Senate, said on French television.
“The results of this Senate election represent a real comeuppance for the right.”