The Ipsos survey gave Ms Le Pen’s anti-immigration party 22 percent of the vote while the embattled French President’s group, La Republique En Marche (LREM), fell behind on 21 percent. It is the first time an Ipsos poll was topped by RN, although recent daily surveys had suggested Ms Le Pen’s group is the most popular. Between May 2 and 3, 1,500 people took part in the poll after Mr Macron announced a series of tax cuts worth £4.27 billion (€5 billion) to appease the “yellow vests” protesters.
The support enjoyed by the young president’s party slipped from 23 percent in April.
Mr Macron has in recent months faced fierce criticism over his handling of the yellow vests movement which sprung up in November in protest over his polices which were seen as favouring the rich.
French voters will head to the ballot box on May 26 and the chances of Mr Macron winning their support with his pro-European agenda is shrinking fast.
RN, formerly known at the National Front, is among a string of populist groups across Europe who are planning to join forces to establish a Eurosceptic bloc of MEPs in the EU parliament.
Ms Le Pen is a close ally of Italy’s interior minister Matteo Salvini and Hungary’s prime minister Viktor Orban.
During a visit to Bulgaria last week, she praised Mr Salvini for “controlling” Italy’s problem with mass migration.
Europeans who are fed-up with slow economic growth and the threat of Islamist militants arriving on their shores are flocking to support populist parties.
Mr Macron, 41, is facing a tough challenge from Ms Le Pen, who is urging voters to get behind far-right parties to “change Europe from the inside”.
She has also called on Belgians to back the Flemish far-right party Vlaams Belang.
French film stars Juliete Binoche and Emmanuelle Beart were among 1,400 people from the arts and showbiz world to publicly back the yellow vests.
They put their names to an open letter calling for the protesters’ demands including greater social justice and an overhauled tax system to be honoured.
The group also criticised the tough stance police have taken in response to the demonstrations, which began in November in Paris and have since spread to cities across the country.