The organisation was formally launched at a founding congress and adopted the name Peaceful Russia, Yashin said on social media on Monday.
The party said it sought to represent "Russia's interests," in contrast to the policies pursued by President Vladimir Putin.
"By those interests, we mean withdrawing troops from Ukraine and rejecting imperialism, guaranteeing human rights and freedoms, and ensuring a just social order," the statement said.
Yashin was elected chairman of Peaceful Russia.
Olga Podolskaya, a former regional MP from Russia's Tula region, was elected deputy chair.
Yashin was imprisoned in Russia but was released in 2024 as part of a huge prisoner exchange between Russia and the United States.
Russia's exiled opposition has struggled with its inability to influence political developments inside the country.
It remains divided by personal and political rivalries despite efforts to build a united front against Putin.
Among the guests at the party congress were Leonid Volkov of the Anti-Corruption Foundation (FBK) founded by late opposition leader Alexei Navalny, who died in prison in 2024, and Marat Gelman of the Russian Anti-War Committee.
Another platform bringing together members of the Russian opposition in exile is a dialogue initiative established by the Parliamentary Assembly of the Council of Europe.
Memorial, a Russian human rights group that has been banned in Russia, also continues its rights advocacy and educational work from abroad.
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