In large advertisements in major newspapers, the Victorian Women's Trust said the unwed, atheist Gillard had faced enmity not only from her political opposition, but members of her own Labour Party and an often hostile media.
"From the outset, and despite its democratic legitimacy, the Gillard-led minority government sparked an unheralded series of hostile reactions from different quarters across the country," it said.
"Her many achievements went largely unproclaimed, while her mistakes were amplified -- and continually referenced."
Gillard became a torchbearer for women around the world with her fiery speech about misogyny on the floor of parliament last October, even as she was subjected to unrelenting comments on her gender.
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Placards such as "Ditch the Witch" were held up at rallies. One radio personality said she should be thrown in the ocean in a chaff bag, and another asked her repeatedly whether her partner Tim Mathieson was gay.
Gillard, who last week was replaced as Labour leader and prime minister by Kevin Rudd, the man she deposed in 2010, has said her gender "does not explain everything about my prime ministership, nor does it explain nothing".
The Women's Trust said the past three years should prompt reflection on "the seams of aggressive contempt and sexist abuse that lay beneath everyday life and which surfaced with Julia Gillard's elevation as Prime Minister".
"We now have a climate in which people willingly and disrespectfully attack one another in anonymous and often vitriolic commentary that is no substitute for mature democratic debate.