A huge rally was held at Paris's Bastille monument in support of Left Front presidential candidate Jean-Luc Melenchon on March 18, the Morning Star said the next day.
More than 100,000 trade unionists, members of the French Communist Party (PCF) and disaffected former members of the Socialist Party (PS) marched under red balloons and flags.
Melenchon said: "We're going to make this election on April 22 a civic insurrection.
"The insurrection is ... the most indispensable of duties in this France disfigured by social, territorial, cultural and gender inequality."
Melenchon, a former PS minister, called for the French people to "to start a new chapter that will enable us to refound the republic.”
He called for a higher minimum wage and higher taxes on the super-rich, full restoration of retirement rights at 60, nationalisation of the energy sector and stronger rights at work.
Melenchon concluded: "Long live universal humanity, long live France, long live the social republic," before leading the crowd in singing the socialist anthem “The Internationale”.
The Morning Star said support for Melenchon has surged from around 5% in October to 11% in the latest polls.