The court on Wednesday upheld his claim that some of his treatment amounted to "inhuman or degrading treatment or punishment", BBC reported.
After the judgment, Breivik's lawyer Oystein Storrvik called for his solitary confinement to be repealed.
Breivik, a right-wing extremist, killed 69 people at a summer camp for young centre-left political activists on the island of Utoeya in July 2011.
Earlier that day, he set off a car bomb in the capital, Oslo, killing eight people.
In her ruling, Judge Helen Andenaes Sekulic said the right not to be subjected to inhuman treatment represented "a fundamental value in a democratic society" and also applied to "terrorists and killers".
Breivik had challenged the government over his solitary confinement, which saw him kept alone in his cell for 22 to 23 hours a day, denied contact with other inmates and only communicating with prison staff through a thick glass barrier.
Judge Sekulic also noted that Breivik had been woken up every half hour at night over a long period of time and on some occasions subjected to strip searches with female officers present, which he found particularly difficult.
"Taken together with the other stringent restrictions to which he was subjecteed, this was regarded as degrading treatment in the Convention sense," said the judge, Norwegian national broadcaster NRK reported.
The court also ordered the Norwegian state to pay Breivik's legal costs of 330,000 kroner ($40,000).