Frigide Barjot told reporters Friday she had been threatened by other more-radical opponents of legalizing homosexual marriages and would likely not take part in Sunday's event.
"I would like to go but my presence crystallizes hatred," said Barjot, who has denied her opposition is not based on homophobia.
She has said she would prefer France adopt a civil union system but prohibit adoption by homosexual couples.
Radio France Internationale said Saturday Barjot had been given police protection.
The French government will have 4,500 officers assigned to Sunday's rally.
France passed the measure allowing same-sex marriage last month.