“We must be willing to make the changes that we know may not necessarily have changed history, but could change the future,” she said at a news briefing.
The man, a Sri Lankan national, stabbed seven people in a supermarket. Three of them are in a critical condition.
The attacker, a known supporter of Islamic State, was shot dead by police.
He has now been identified as Ahamed Aathil Mohamed Samsudeen, a 32-year-old Tamil, who arrived in New Zealand in 2011 and sought refugee status.
Ms Ardern, who described the stabbings as a “terrorist attack”, said she expected that changes to the country’s counter-terrorism legislation would be backed by parliament by the end of September.The legislation is expected to make it easier to convict someone for planning a terror attack.
Samsudeen had been arrested a number of times before Friday’s incident. But Ms Ardern said that every legal avenue to keep him out of the community had been exhausted.