Prime Minister Jacinda Ardern spoke emotionally during the bill's final reading of the traumatic injuries suffered by victims of the March 15 attacks, whom she visited in Christchurch Hospital after the shootings.
Brenton Tarrant, 28, a suspected white supremacist, was charged with 50 counts of murder after the attack on 15 March.
A lone gunman used semi-automatic guns in the Christchurch mosque attacks, killing 50 people as they attended Friday prayers.
"I struggle to recall any single gunshot wounds", Ms Ardern said.
The government has begun work on a second arms amendment bill it hopes to introduce in June, he said, adding that the measure would tackle issues regarding a gun registry, among others. In every case, they spoke of multiple, debilitating injuries.
"They will carry disabilities for a lifetime, and that's before you consider the psychological impact".
"I like to think the vast majority of Kiwis are good law-abiding citizens and both the prime minister and myself have made this very clear that we're not penalising these gun owners, but we have changed the law and as a effect of that they are now holding something which is illegal".
"I could not fathom how weapons that could cause such destruction and large-scale death could be obtained legally in this country".More news: Jennifer Lopez reveals why she hasn't started planning her wedding
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The bill is expected to receive its Royal Assent from the governor on Friday before it becomes law, after which military-style semi-automatics (MSSAs) and assault rifles and associated parts will be illegal.
The law includes a buy-back scheme under which owners of outlawed weapons can surrender them to police by September 30 in return for compensation based on the weapon's age and condition.
"We are ultimately here because 50 people died and they do not have a voice", she said.
The conservative opposition National Party backed the bill at all stages, despite some farmers this week expressing frustration at a lack of exemptions for pest control - and on Wednesday did the same in a rare moment of unity.
Ardern told lawmakers she couldn't face the victims left behind and tell them she was OK with such unsafe weapons being legal to purchase in New Zealand.
"New Zealand will be a safer place once this is implemented and once we get these guns out of our communities", Mr Nash said. The only dissenting voice was from the libertarian ACT Party, which has one lawmaker in Parliament.
"This is one of the most important pieces of legislation we will pass this Parliament because it's not only about keeping people safe, it's about putting a marker in the sand for our New Zealand culture". "We have used that voice wisely", she said to applause from lawmakers. We in this House are their voice. "And if you do not, you should be able to agree that we can move swiftly", she said. "My view is that an argument about process is an argument to do nothing".