“I have carried out the most spectacular and sophisticated attack on Europe since World War II,” Anders Behring Breivik told the court.
Breivik said he would do it all again and asked to be acquitted.
Although he admits the bombing and attack on a youth camp, he has pleaded not guilty to terror and mass murder.
“These acts are based on goodness, not evil,” he said, adding that he had toned down his rhetoric out of concern for the victims.
As he closed his statement, pressed by the judge, Breivik said that he acted to defend Norway against immigration and multi-culturalism.
After a lunch break, the prosecution began its cross-examination of Breivik. Topics covered include his choice of uniform and his claim to be a member of the Knights Templar group, which the prosecution has previously asserted does not exist.
Breivik insisted the group did have a few members, but conceded that the language he used to describe it may have been “pompous”. He also implied that he drew inspiration for his strategies from al-Qaeda.
Earlier, Breivik’s lawyers warned that many Norwegians would find his comments upsetting. Geir Lippestad also said that he understood concerns by victims’ families that Breivik would use his trial as a pulpit, but added that Breivik had a right to explain himself.
His testimony and that of his witnesses will not be broadcast. His testimony is expected to last for five days.
The BBC’s Matthew Price in the courtroom says that Breivik’s evidence will be crucial in working out if he is criminally insane and psychiatrists in court have been observing him closely.
One of the questions at the very heart of this trial, which is expected to last for 10 weeks, is Breivik’s mental state. He has already said that he does not recognise the court.
Despite repeated interruptions from the judge to cut down his speech, Breivik insisted that he had more to say, although he agreed to limit his comments to Norway.
Breivik’s comments have ranged from vehement criticisms of liberalism and multi-culturalism to claims that he “supports the model in South Korea and Japan”.
Our correspondent says his comments about Norway fit in with his belief that liberal ideals are ruining Norway and are the reason why he attacked the governing Labour party summer camp on Utoeya island and government offices.
“I am not scared by the prospect of being in prison all my life. I was born in a prison where I could not express my beliefs,” he told the court, adding: “This prison is called Norway”.
Breivik said he was speaking as a representative of a Norwegian and European “resistance movement”.
As the day began, the court was briefly adjourned and one of three lay judges dismissed for saying last July that Breivik should face the death penalty.
A lay judge is an ordinary member of the public who forms part of the judgement panel. Thomas Indreboe was replaced by a substitute lay judge who observed proceedings yesterday.
On Monday, prosecutors played harrowing recordings of the events and described the fate of each victim in detail.
Throughout the evidence, Breivik remained emotionless, although he shed tears when the court played a 12-minute anti-Islam video which he had posted online on the day of the carnage.
Breivik’s lawyer later said that his client appeared to have cried over feelings that his attacks were “cruel but necessary… to save Europe from an ongoing war”.
Breivik detonated a bomb in a van parked outside government offices in Oslo on 22 July, killing eight people.
He then travelled to Utoeya where, dressed as a police officer, he shot dead a further 69 people who were attending a youth camp run by the governing Labour party.
The 33-year-old Norwegian was found insane in one examination, while a second assessment made public last week found him mentally competent.
If the court decides he is criminally insane, he will be committed to psychiatric care; if he is judged to be mentally stable, he will be jailed if found guilty.
If jailed, he faces a sentence of 21 years which could be extended to keep him behind bars for the rest of his life.
The courtroom has been specially built for the trial to accommodate more than 200 people. Glass partitions have been put up to separate the victims and their families from Breivik.