In a surreal twist to the saga over Depardieu's move into tax exile, the veteran animal rights campaigner said she would emulate his request for Russian nationality unless authorities intervened to save Baby and Nepal.
The two elephants face being put down because they have been diagnosed with tuberculosis and have been deemed a threat to the health of other animals and visitors to the Tête d'Or zoo in Lyon.
City authorities ordered the elephants to be put down last month but a petition organised by their original owner, circus master Gilbert Edelstein, resulted in them being granted a temporary reprieve over Christmas.
Bardot said in a statement she would be leaving France if the reprieve was not made permanent.
"If the powers that be have the cowardice and the shamelessness to kill Baby and Nepal… I have decided to take Russian nationality and quit this country that is nothing more an animal cemetery," Bardot said.
Bardot, 77, has been a high-profile supporter of Depardieu in his spat with the French government over his decision to take up residence in neighbouring Belgium for tax reasons.
She said last month that her fellow actor, who was branded "pathetic" by Prime Minister Jean-Marc Ayrault, had been the "victim of extremely unfair persecution".