The far-right extremist, who killed 77 people in Norway in July 2011, has argued the conditions of his detention are “inhumane”.
Breivik appealed to the ECHR after the Norwegian Supreme Court refused to hear a case last year against a ruling that his near-isolation in a three-room cell respected his human rights.
His lawyer argues that his prison conditions violate articles 3 and 8 of the European Convention on Human Rights. The former prohibits inhuman or degrading treatment, the latter guarantees a right to a private and family life.
At the time Breivik's appeal was filed his lawyer, Øystein Storrvik, told AFP that the case focused on the issue of isolation.
Norway has repeatedly rejected allegations that Breivik is isolated, arguing that he is treated as a “VIP prisoner” and has regular contact with prison staff, his lawyer and visitors.
Breivik, 39, was sentenced in 2012 to 21 years in prison, which can be extended indefinitely as long as he remains a threat to society.
His killing spree took place on July 22nd, 2011, when disguised as a police officer and armed with a semi-automatic rifle and pistol, he killed 69 people, most of them teenagers who were attending a Labour Party youth camp on the island of Utøya.
Just a few hours before the camp attack, he killed eight people in a bombing outside a government building in Oslo.
The ECHR ruling will be made public on Thursday at 10am and will be broadcast on its website.