Anders Behring Breivik said at his trial today his shooting and bomb attacks were "sophisticated and spectacular" and that he would do the same thing again.
Mr Breivik, 33, has pleaded not guilty and said he was defending his country by carrying out the attacks.
He set off a car bomb that killed eight people at government headquarters in Oslo last July, then killed another 69 people in a shooting rampage at a youth summer camp organised by the ruling Labour party.
Taking the stand at his trial for the first time, Mr Breivik read a statement for an hour, ignoring pleas from the judge to stop and sparking criticism from victims he was being allowed to use the trial for violent propaganda.
The killer invoked Native American warriors such as Sitting Bull, raged against Islam and multicultural "hell" and warned of "rivers of blood" in Europe.
"I have carried out the most sophisticated and spectacular political attack committed in Europe since the Second World War," Mr Breivik told the court in a monotonous, unemotional voice.
"They [Norwegians] risk being a minority in their own capital in their own country in the future."
"Yes, I would have done it again, because offences against my people ... are many times as bad," he said.
While he has admitted the killings and will likely be kept behind bars for the rest of his life, Mr Breivik's main objective is to prove he is sane, a court judgment that he sees as vindicating his anti-Muslim and anti-immigration cause.
The high school dropout has said being labelled insane would be a "fate worse than death."
If found guilty and sane, Mr Breivik faces a maximum 21-year sentence but could be held indefinitely if he is considered a continuing danger. If declared insane, he would be held in a psychiatric institution indefinitely with periodic reviews.
Norway does not have the death penalty.
Mr Breivik's testimony was not broadcast on television due to concerns that the gunman could use the trial as propaganda for his violent cause.
The day began in controversy after the court dismissed a lay judge after he posted a comment on a Facebook page days after the massacre saying the gunman should face the death penalty.
Two professional judges, as well as three lay judges chosen from civil society, preside over the court. The judge, who will be replaced, posted: "The death penalty is the only just outcome of this case" on a web page.
Mr Breivik appeared for the first time in court yesterday, giving a clenched-fist salute, smirking at the court and pleading not guilty.
He listened impassively for hours as prosecutors read out an indictment detailing how he massacred teenagers trapped on an island resort outside Oslo. He only shed tears when the court later showed one of his propaganda videos.
Mr Breivik shot most of his victims several times, often using the first shot to take down his target then following up with a shot to the head.
His youngest victim was 14. He later surrendered as "commander of the Norwegian resistance movement".
The trial is scheduled to last 10 weeks.
More than 200 people sat in the specially built courtroom while about 700 attack survivors and family members of victims watched on closed-circuit video around the country.
Mr Breivik’s defence team has called 29 witnesses to argue he was sane, with a world view shared by a narrow group of people.
His proposed witnesses include Mullah Krekar, the Kurdish founder of Islamist group Ansar al-Islam, who was recently jailed in Norway for making death threats, and "Fjordman", a right-wing blogger who influenced Mr Breivik.