Fifty-one people were killed and 49 injured in March a year ago when Australian gunman Brenton Tarrant opened fire during Friday prayers.
Tarrant was scheduled to go to trial on the charges in June.
Brenton Tarrant changed his plea from not guilty to guilty in an appearance by video link in the High Court at Christchurch this morning.
Tarrant, a former gym instructor from Australia, has maintained a not-guilty plea throughout.
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Aya Al-Umari, whose brother Hussein Al-Umari was killed in the Al Noor mosque shooting, holds a pendant with a photo of herself and Hussein during an interview at her home in Christchurch, New Zealand.
The change in plea came less than two weeks after New Zealanders commemorated those who died during the attacks on March 15, 2019.
"The guilty pleas represent a very significant step towards bringing finality to this criminal proceeding", he said.
In a rambling manifesto posted online before the killing spree, Tarrant said he had moved to New Zealand with the specific aim of conducting an atrocity against Muslims. The country is beginning a four-week lockdown with the hopes of decreasing the disease's transmission.