The law sets a prison sentence of 12 to 30 years for anyone convicted in the "aberrant" killing of a woman or girl in domestic violence, or because of her gender. It also describes those killings as femicides.
Even longer sentences can be set in the killing of a woman who is pregnant or recently gave birth, girls under 14, women who are over 60 or disabled, and killings committed in the presence of the victim's child or parent.
At the law-signing ceremony, Rousseff said that 15 women are killed daily in Brazil, many through domestic violence. She added that an estimated 500,000 women and girls are raped annually in Brazil, but only about 10 per cent of those crimes are reported.
"The numbers scare us," said the president, adding that Brazilian women of all social classes are at risk for such violence.
Countries such as Guatemala, El Salvador and Guatemala have passed similar laws in recent years in an effort to combat domestic violence.