Russian socialite Ksenia Sobchak is to stand in the country's presidential election in March, when Vladimir Putin is widely expected to run again.
Ms Sobchak conceded she was an unlikely candidate and said she supported opposition leader Alexei Navalny, who is barred from standing.
However he had warned her not to stand and some commentators now predict an opposition split.
The Kremlin welcomed her candidacy, saying it was fully constitutional.
Mr Navalny is currently serving a 20-day prison sentence for his role in organising "unsanctioned" protests.
He is banned from the election because of .
Ms Sobchak, who is also a journalist and TV presenter, called for the bar on him standing to be lifted.
She said she wanted to be "a mouthpiece for those who cannot be candidates".
"I am against revolution but I am a good middleman and organiser," Ms Sobchak wrote in a letter published on the website of Vedomosti business daily.
Russia's election campaign starts around 7 December, when political parties are expected to hold congresses to nominate their candidates.
A Russian citizen not backed by a political party has the right to register as an independent presidential candidate provided he or she collects at least 300,000 signatures.
President Putin, who first took office as president in 2000, has not announced yet whether he will stand again.