Parliament also passes a bill increasing the punishments for some rape offences, mandating DNA testing and making the rape of a minor or the disabled punishable by life imprisonment or death.
A joint session of Pakistan's lower and upper houses of parliament, broadcast live on television, approved a new anti-honour killing law, removing a loophole in existing law that allows killers to walk free after being pardoned by family members.
The assembly also passed a bill increasing the punishments for some rape offences, mandating DNA testing and making the rape of a minor or the disabled punishable by life imprisonment or death.
"Laws are supposed to guide better behaviour, not allow destructive behaviour to continue with impunity," said former senator Sughra Imam, who initially put forward the bill.
Women have long fought for their rights in Pakistan, where rape conviction rates are close to zero percent, largely due to the law's reliance on circumstantial evidence and a lack of forensic testing.
Honoring all the women (and men) who died in the name of honor. Pakistani finally passes anti-honor killing bill. https://t.co/fzW1nGnkd4— Bina Shah (@BinaShah) October 6, 2016
Rights groups and politicians have for years called for tougher laws to tackle perpetrators of violence against women in the country.
Filmmaker Sharmeen Obaid-Chinoy won an Oscar earlier this year for a documentary on honour killings that was hailed by Pakistan's Prime Minister Nawaz Sharif, who promised to push through the legislation in February.
Thank you to PM Nawaz Sharif for keeping his promise:#antihonorkilling bill— Sharmeen Obaid (@sharmeenochinoy) October 6, 2016
Obaid-Chinoy posted on Twitter: "Thank you to PM Nawaz Sharif for keeping his promise".
The death of social media star Qandeel Baloch, judged by many in the country as infamous for selfies and videos that by Western standards would appear tame, reignited polarising calls for action after her brother admitted killing her.
"I am not embarrassed at all over what I did," he told media at a defiant press conference in July. "Whatever was the case, it (his sister's behaviour) was completely intolerable."
"This is a step in the right direction," women's activist and columnist Aisha Sarwari said about the passage of the bill. "We should take our little wins where we get them and proceed forward and not retreat."
But rights activist Farzana Bari was more cautious, saying the bill still allowed a judge to decide whether a murder qualified as an "honour killing" or not.
Marvi Sirmed, feminist and rights activist, called the bill "very good news", but echoed Bari's concern, saying: "The challenge now is, how the honour crimes be defined."
Prime Minister Nawaz Sharif later issued a statement hailing the passage of the bill and vowed police and courts would implement it.
"We will make... sure to fully enforce this legislation across the country," a statement issued by his office said. "Women are the most essential part of our society and I believe in their empowerment, protection and emancipation."
"These bills are hugely important for Pakistani women, where rape conviction rates were almost non-existent, due in large part to various technical obstacles to accessing justice," said Yasmeen Hassan, Global Executive Director at Equality Now.
"We hope that these new laws will help generate a cultural shift in Pakistani society and that women will be able to live their lives in safety," Hassan added.
Some 500 women are killed each year in Pakistan at the hands of family members over perceived damage to "honour" that can involve eloping, fraternising with men or any other infraction against conservative values relating to women.
In most cases, the victim is a woman and the killer is a relative who escapes punishment by seeking forgiveness for the crime from family members.
A 2005 amendment to the law pertaining to honour killings prevented men who kill female relatives pardoning themselves as an "heir" of the victim.
But punishment was left to a judge's discretion when other relatives of the victim forgive the killer — a loophole which critics say had been exploited.
The amendments passed Thursday and published on the National Assembly website mandate judges to sentence someone who kills in the name of "honour" to life imprisonment, even if they have been forgiven and thereby avoid the death penalty, said senior opposition lawmaker Farhatullah Babar.
"Even if the close family members pardon the murderer, the court is bound to send him to jail for 25 years," Babar told AFP.
The amendments regarding rape, in addition to calling for DNA tests and toughening the punishment in some cases, also protect a victim's identity and mandate that cases be brought to court within three months.