Tarrant, a 28-year-old licenced gun owner, did not enter a plea as he appeared in court on Saturday. A single murder charge was filed against him, with further charges expected to follow.
Forty-nine people were killed and dozens more wounded in the mass shootings at two mosques. Five weapons were used, including two semi-automatic weapons.
A further two suspects are in police custody, as authorities look to determine if they played a role in the attacks, which have been described as the worst peacetime mass killing in New Zealand’s history.
None of those arrested has a criminal history in New Zealand or Australia.
At press conference on Saturday, Ardern said she would look at banning semi-automatic firearms.
“I can tell you one thing right now: our gun laws will change,” said Ardern. “There have been attempts to change our laws in 2005, 2012 and after an inquiry in 2017. Now is the time for change.”
The government has raised the country’s security threat to the highest level.
Tarrant, who cited France as an inspiration for the attack, is due reappear in court on 5 April.