The West African nation's constitution has prohibited violence against women since 2009 but police have been powerless to act in cases where victims abused at home were unwilling to come forward.
"This law will significantly contribute to a change in behaviour within Guinean families," said Aba Serra, president of the National Assembly's women's affairs committee.
Women face significant discrimination in Guinea-Bissau and are denied equal pay, education and opportunities, with the majority unable to read or write.
Charities say domestic violence, child marriage and female genital mutilation, outlawed in 2011, remain widespread.
"Thirty women die each year at the hands of their husbands and the trend is growing very fast. We have to put a stop to this," said Fatoumata Djau Balde of the government-run National Committee for the Abandonment of Harmful Practices. While the vast majority of cases of domestic violence involve men abusing women, Balde said the law would apply equally to both sexes.
"It's about violence in the home, perpetrated against men as well as women. These acts are (now) considered a public crime," she said.
"That is to say, in cases of violence in the home, if the man or woman does not file a complaint, the neighbours can do it for them, and the law will be applied."
There are no definitive statistics on domestic violence in Guinea-Bissau but the government-run Institute for Women and Children estimates that almost 60 percent of women experience physical or sexual abuse at least once.
"This type of violence is practised everywhere in the countryside and more and more in urban areas. Women living in poverty are more defenceless against this kind of abuse and exploitation," a report by the institute concluded.
Penalties for those who fall foul of the new Law Against Domestic Violence range from two to 12 years in prison.