Pakistan's government has closed a loophole allowing those behind so-called honour killings to go free.
New legislation means killers will get a mandatory life sentence.
Previously, killers could be pardoned by a victim's family to avoid a jail term. Now forgiveness will only spare them the death penalty.
It is being seen as a step in the right direction in a country where attacks on women who go against conservative rules on love and marriage are common.
According to the independent Human Rights Commission of Pakistan (HRCP), nearly 1,100 women were killed by relatives in Pakistan last year in such killings, while many more cases go unreported.
The loophole allowed the perpetrators of "honour killings" - often a relative acting on the pretext of defending family "honour" - to avoid punishment because they can seek forgiveness for the crime from another family member.
Pakistan and 'honour killings'
In recent months, a number of high-profile deaths have made headlines both in Pakistan and abroad, including the killing of British woman Samia Shahid in July, allegedly by her father and her former husband.
The same month, Pakistani social media celebrity Qandeel Baloch was strangled to death, allegedly killed by her brother in the province of Punjab.
The amended law was debated by Pakistan's National Assembly for four hours on Thursday, before being passed unanimously.
Campaigners have been calling for tougher legislation to protect women from violence for years.
A 2005 amendment to the law pertaining to "honour killings" prevented men who kill female relatives pardoning themselves as an 'heir' of the victim.
Pakistani activist and filmmaker Sharmeen Obaid - who won an Oscar earlier this year for a documentary on "honour killings" - paid tribute to the people who had worked to get the bill through.
"It may not change much over night but it is certainly a step in the right direction," she said in a Facebook post. "And today I am proud that we have gone the distance on this bill."
Others were more cautious, raising concerns over the fact the bill still allows a judge to decide whether a murder qualifies as an 'honour killing' or not.
A controversial law which may prove a deterrent: By M Ilyas Khan, BBC News, Islamabad
The bill - pending for a long time - has now been passed by both houses of parliament, which means they will soon make it to the statute books.
But it is yet to be seen how effective a deterrent the anti-honour killing law may prove.
The crime is often committed either as a result of sudden provocation or under tremendous social pressure. Killers have largely enjoyed impunity due to a legal provision under which a relative of the victim could pardon the perpetrator.
That clause has now been tweaked to ensure the offender pays the price. This may prove to be a deterrent in the long run.
In rape cases, the parliament has for the first time introduced a provision allowing DNA tests to ascertain identity of the offender. Experts believe this will effectively cover up for the weakness in the previous legislation that relied heavily on circumstantial evidence.