Le Pen would top the first-round vote with between 34 percent and 36 percent depending on the scenarios tested by pollster Toluna Harris Interactive in a survey carried out between November third and fifth, Reuters reported.
A similar poll last month showed her at between 35 percent and 37 percent.
Melenchon, the candidate of the far-left France Unbowed (LFI) party, is seen reaching a run-off in all five scenarios polled, with either 18 percent or 19 percent.
Le Pen is seen beating Melenchon easily in a run-off.
As Macron’s second and final five-year term comes to an end, the unpopular president leaves behind a hollowed-out political center and weak economy, creating an opening for hard-line parties.
Melenchon has already run three times for president in 2012, 2017 and 2022, but never managed to reach the second round. Le Pen also ran in those same three elections and lost in the second round in 2017 and 2022 to Macron.