Kobre & Kim has agreed to advise Russian oligarch Roman Abramovich on judicial and administrative proceedings.
Abramovich has been sanctioned by the UK and European Union for his cozy ties with Russia's strongman Vladimir Putin.
At the request of Ukraine president Volodymyr Zelensky, the US did not sanction the billionaire.
American officials did issue a warrant in June to seize Abramovich's Boeing 787 Dreamliner and Gulfstream jet because they flew to Russia.
In its federal filing, K&K notes that Abramovich is acting as a mediator in the peace negotiations between Russia and Ukraine. Both countries approved of his role as mediator.
Abramovich "has been heavily involved in advocating for, and coordinating the establishment of humanitarian corridors and other humanitarian rescue missions," the filing notes.
K+K's registration statement says Abramovich is a citizen of Russia, Israel and Portugal.
He chairs the Federation of Jewish Communities of Russia and serves as a trustee of the Moscow Jewish Museum.
During the past 15 years, Abramovich has donated more than $500M to Jewish causes throughout the world.