The move comes as far right parties across the continent, divided into two main groups inside the European Parliament, grapple with how they might coalesce into a more cohesive force ahead of a June vote in which polls show populists making gains.
Polls show the European Conservatives and Reformists Group (ECR), which also counts Poland's Law and Justice, Spain's Vox and Finland's The Finns among its ranks, may overtake French President Emmanuel Macron's Renew Europe party in size.
"Reconquete shares ECR's political DNA! The real political right which acts upon its convictions: defence of the identity of nations and our civilisation when faced with immigration and Islamisation, defence of economic freedoms, ...the safeguarding of our values against wokeism," Reconquete co-chair Marion Marechal said on Wednesday.
Marechal is the niece of Marine Le Pen, leader of France's biggest far-right party, Rassemblement National (National Rally), which is aligned with the hard right Identity and Democracy (ID) group in the European Parliament.
A late January opinion survey for Les Echos newspaper showed Reconquete winning 7% of voter support in France compared with 27% for the Rassemblement National.
Analysts say Europe's far right will remain somewhat hobbled as a political force if the two factions do not work together.
Veteran Hungarian leader Viktor Orban has said his Fidesz party is in talks to join ECR, though not before the June elections. Orban, who maintains close ties to Moscow despite its invasion of Ukraine and for weeks stood in the way of a European financing package for Kyiv, would likely bring a sizeable cohort of lawmakers.
"There is the possibility that Fidesz will converge towards the ECR group if it supports our Euro-Atlantic stance," Carlo Fidanza, a eurodeputy with Meloni's Brothers of Italy party, told Reuters.
However, Orban would also bring risks for Meloni, whose stature as a European leader alongside Macron and German Chancellor Olaf Scholz has grown at past EU summits.
"How successful (Meloni) is will rest on her ability to ... engage the EU's periphery while being a core member," Eurointelligence wrote in a briefing note.
Marechal's Reconquete party was founded by Eric Zemmour who ran for president in 2022 on a nationalist programme promising to save France from a downward spiral that he blamed largely on what he described as unfettered immigration and the increasing influence of Islam. He holds several convictions for inciting racial hate.
(Reporting by Elizabeth Pineau, Richard Lough and Angelo Amante; Editing by Nick Macfie)
