Fifty-one people were killed in the shootings at Al-Noor and Linwood mosques in the South Island city, reports Efe news.
"A charge of engaging in a Terrorist Act under section 6A of the Terrorism Suppression Act 2002 has now been filed against Brenton Tarrant," Police Commissioner Mike Bush said in a statement.
An additional charge of murder and two of attempted murder have also been filed, Bush said.
The 28-year-old now faces 51 charges of murder and 40 of attempted murder, as well as the terrorism charge.
The police met the victims families and survivors to inform them of the new charges and update them on the ongoing investigation and court process to come, Bush said.
Tarrant is being held at Auckland's high-security prison at Paremoremo. He appeared via video link in Christchurch High Court on April 5 where the judge ordered two mental health evaluations to be completed to assess his fitness to enter pleas.
Tarrant is expected to reappear in court on June 14.
New Zealand Parliament passed a gun reform bill on April 10, which was enacted days after the shootings.
Tarrant had obtained a firearms license in November 2017 after passing all legal requirements.
The accused live-streamed the mosque attack for 17 minutes on social media, which was shared across online platforms around the world, leading New Zealand Prime Minister Jacinda Adern to spearhead an effort to get both governments and tech companies to improve their efforts to tackle extremist content.