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.
Do you know what else is “a fundamental value in a democratic society?” Not killing 77 innocent people.