Brenton Tarrant has admitted that he was the was lone gunman who murdered 51 Muslims at two Christchurch mosques in 2019, ending the need for a trial.
Tarrant gunned down his victims at the mosques during Friday prayers on March 15 in 2019 and livestreamed the first attack on Facebook.
The shootings killed 51 people and wounded 49.
Australian-born Tarrant admitted, in a High Court hearing in Christchurch on Thursday, to carrying out the attacks.
The 28-year-old has been described as a white supremacist.
Tarrant was later charged with 51 murders, 40 attempted murders, and engaging in a terrorist act and had pleaded not guilty to all charges.
The trial had been due to start on June 2.
A sentencing date is yet to be set.
Tarrant began his rampage at the Al Noor Mosque, in the Christchurch suburb of Riccarton, about 1.40pm local time (11.40am AEDT) and continued at Linwood Islamic Centre about 1.55pm.