The court also found him to be sane, dismissing the prosecution's request for an insane verdict, reported Xinhua.
Norway's penal code does not have the death penalty or life in prison, and the maximum prison term for Breivik's charges is 21 years.
However, inmates who are considered a threat to society can be held indefinitely.
District Court Judge Wenche Elizabeth Arntzen first read out the conclusion of the verdict.
After being brought into the main courtroom, Breivik smiled and chatted with his lawyers and people behind him before the verdict reading started at 10 a.m.
Norwegian prosecutors had demanded that Breivik be ruled as insane when the trial for Norway's worst peace time attacks started April 16.
Breivik's defense lawyer Geir Lippestad, who met Breivik Thursday for the last time before Friday's verdict, said that Breivik would accept prison terms but would appeal an insanity ruling.
Breivik, a 33-year-old Norwegian on a mission to expel Muslims from Europe, set off a car bomb that killed eight people outside government headquarters in Oslo July 22, 2011 and then killed 69 others in a shooting rampage on Utoeya island, where young members of the governing Labor Party had gathered for their annual summer camp.