The 16 parties said in a joint statement published by Le Pen's National Rally (RN) that it was the "first stone" in the construction of such an alliance to "reform Europe".
Signatories included Matteo Salvini, leader of Italy's anti-immigration League, Santiago Abascal of the Spanish populist movement Vox and Jaroslaw Kaczynski, leader of Poland's governing PiS party.
"At a time when globalists and pro-Europeans, of whom Emmanuel Macron is the main representative in France, are launching the Conference on the Future of Europe that aims to increase the power of European bodies, today's agreement is the first stone towards the formation of a grand alliance in the European Parliament," they said.
The parties are currently not part of the same groupings in the European Parliament, while Hungary's ruling Fidesz party quit the European People's Party (EPP) group, the biggest in the parliament, in March.
The EU "continues to pursue the federalist path that inexorably distances it from the peoples who are the beating heart of our civilisation," they wrote.
They urged "reform" of the bloc, adding that Europe's "most influential patriotic parties" had "understood the importance" of joining forces.
Salvini called the declaration "a charter of values" to imagine a European future "based on freedom and identity rather than on bureaucracy and standardisation".
"It is a further step towards building a solid, extended and alternative alliance to the illiberal left of taxes and out-of-control immigration," he added.
Other prominent far-right parties involved include the FPOe of Austria and Belgium's Vlaams Belang, the RN said.
Hard right and far-right parties have consolidated their positions across Europe in recent years, even if there have been tentative signs that their popularity could be waning in some places.
Le Pen's RN suffered a major disappointment in regional elections last month by failing to grasp control of a French region for the first time, as several polls had suggested.
Le Pen said the declaration would form the "basis of a common cultural and political work, respecting the role of the current political groups."
She reiterated her call for "deep reform" of the EU and her fears over the "creation of a European superstate."
Spanish MEP Iratxe Garcia Perez,head of the Socialist & Democrats grouping in European parliament, said the extreme right had "a twisted vision of patriotism" which excludes "anyone who doesn't think like them".
"I do not think that this extreme right, populistic and nationalistic alliance will last very long," he added.
"Europe can't be built on confrontation, but rather on cooperation."
