On Tuesday, Ms. Sobchak dismissed any links between her campaign and the Kremlin, but stopped short of criticizing Mr. Putin directly.
“I will not insult him personally,” Mr. Sobchak said of President Vladimir V. Putin, who is widely expected to announce his candidacy for a fourth presidential term. “For me, he is somebody who helped my father in a very difficult situation, basically saved his life,” she said. “But it doesn’t mean that I like everything he does as a politician.”
Ms. Sobchak’s father, Anatoly A. Sobchak, was the reformist mayor of St. Petersburg in the early 1990s when he launched Mr. Putin’s political career by appointing him his deputy. Mr. Sobchak, who was defeated in 1996, was later permitted to travel to France for medical treatment thanks to Mr. Putin, despite warrants for his arrest on corruption charges. The charges were eventually dropped and Mr. Sobchak died a few years later of a heart attack.
Mr. Putin’s leading critic and strongest potential opponent is the anti-corruption campaigner Aleksei A. Navalny, but he is barred from appearing on ballots next March because of fraud convictions that he and rights advocates have dismissed as politically motivated.
Ms. Sobchak promised that she would halt her presidential bid in the event that Mr. Navalny was allowed to run, though analysts regard that as unlikely.
She faces some hurdles of her own before she can become a full-fledged and registered candidate. By Russian law, she either has to collect 300,000 signatures from at least 40 Russian regions, collect 100,000 signatures if she is the nominee of a registered political party, or simply secure the nomination from one of the four parties in the Russian Parliament, or Duma.
In 2011, a Russian oligarch, Mikhail D. Prokhorov, challenged Mr. Putin in the presidential election, saying he would represent the disenchanted voices of Russia’s liberal class. Mr. Prokhorov added spark but managed to get only about 8 percent of the vote, including more than 20 percent in Moscow. But he could never shake perceptions that he was a Potemkin candidate and disappeared from the political scene shortly after Election Day.
While Ms. Sobchak said she would not criticize Mr. Putin personally, she was not shy about rejecting one of his signature policies.
“From the point of view of international law, Crimea is Ukrainian,” she said, citing the 1994 Budapest Memorandum. “Let’s discuss what will happen next to people living in Crimea. There are many Russians there, who supported what happened.”
Restoring good relations with Ukraine is, she concluded, “the most important task that lies before Russia.”
Ms. Sobchak introduced as her campaign chief Igor Y. Malashenko, the co-founder of Russia’s first independent television network and the man behind President Boris N. Yeltsin’s 1996 re-election campaign. She also named to her campaign staff Vitali Shkliarov, who worked on Bernie Sanders’s 2016 presidential campaign.
Ms. Sobchak refused to say how much money her campaign would spend or how she would raise the money, saying only that she has deep-pocketed financial backers.