Since the mid-1970s, she has counseled and advocated for rape victims, organized against "the media's promotion of violence against women", served on the legal team for the plaintiff in a precedent-setting sexual harassment case, founded an international non-governmental organization fighting prostitution and trafficking in women and children, directed the nation's largest legal services program for victims of domestic violence, advocated for the enactment and implementation of laws that further the rights of abused women, and represented hundreds of women victimized by intimate partner violence, human trafficking, sexual assault, the threat of honor killing, female genital mutilation, forced and child marriage, and the internet bride trade.
From 1979 through 1983, she served as a leader and spokesperson for WAP, during which time she joined Gloria Steinem and other feminist leaders in initiating a suit against Hustler and Larry Flynt, appeared on numerous television and radio programs, organized educational events, and spoke in Washington D.C. before the U.S. Attorney General's Commission on Pornography (a.k.a.
Under Leidholdt's leadership since 1994, the center has become the largest legal services program for domestic violence victims in the country.
It has grown from two to twenty-four lawyers and eight support staff members, and has strengthened its advocacy efforts on behalf of under-served populations of women, especially those in New York City's immigrant communities.
On 6 December 1996, in a special session commemorating the abolition of slavery, Leidholdt and a survivor of sex trafficking together addressed the General Assembly of the United Nations.