Valentina Matviyenko has won a seat in Russia's upper house of parliament, the Federation Council.
It is thought Mr Putin and President Dmitry Medvedev want her to be speaker - the third-ranking job in Russia.
But opponents denounced her victory - with more than 95% of the vote - as fraudulent.
Opposition observers claimed to have witnessed ballot-stuffing during the vote in two municipalities of St Petersburg.
"This is a 100% fraud, not a vote," said opposition leader Boris Nemtsov on his blog.
Ms Matviyenko has been governor of St Petersburg, Russia's second city, since 2003.
The city is where both Mr Putin and Mr Medvedev come from.
Ms Matviyenko must be elected by the Federation Council if she is to fill the vacant speaker's position - but the house is loyal to the Kremlin.
If successful, it is thought Ms Matviyenko would be Russia's highest appointed stateswoman since Catherine the Great, who was empress of Russia in the 18th Century.