"For all those who ask who the model was for Marianne, it's a mix of several women, but particularly Inna Shevchenko," Olivier Ciappa, one of the stamp's designers, said on his Twitter account.
The 23-year-old Shevchenko, who has been granted political asylum in France, is the leader of the French branch of Femen, a group which began in Ukraine and describes itself as "radical feminist".
It is best known for topless protests and frequently targets Catholic or Muslim religious authorities.
Most of its activists are in their twenties and some older feminists dismiss Inna Shevchenko as an attention-seeking youngster who has little understanding of relevant women’s issues in France.
Shevchenko was also loud in her condemnation of those in France who opposed gay marriage.
Some feel that she is a divisive figure and not a good choice as the model for a French stamp.
On Monday, the leader of the France’s newly-formed Christian Democratic Party called for a boycott of the new stamp.
Aside from Shevchenko, Olivier Ciappa also named French actress Marion Cotillard and Justice Minister Christiane Taubira as sources of inspiration for the stamp, which was co-designed by artist David Kawena.
Marianne was not a real person but has become a symbol of the French revolution and of freedom, providing inspiration for countless statues, sculptures and paintings.
Wearing a bonnet and always bare-breasted, she has also been a fixture of French stamps for decades, and artists are regularly asked to design new versions of the revolutionary symbol.
She is perhaps best known as the woman waving a French flag in Eugene Delacroix's famous painting "Liberty Leading the People."
"For me, Marianne, who is represented bare-breasted, would probably have been a Femen in 1789 (the French Revolution) because she fought for the Republic's values -- liberty, equality and fraternity," Ciappa said.
Shevchenko, who came to France last August, said she had been unaware she was an inspiration for the stamp.
"Now all homophobes, extremists, fascists will have to lick my ass when they want to send a letter," she added with typical provocation on her Twitter account.
"France always recognised women fighting... (It) is a symbol for all the world," said the activist, who fears persecution in Ukraine after sawing down a wooden cross in Kiev, in a stunt intended to support Russian band Pussy Riot.
President Francois Hollande asked a group of 15 and 16 year old school students to choose the stamp from a selection designed by different artists. It was unveiled at an official ceremony on Sunday, Bastille Day.