Zaniar Matapour, who pledged allegiance to the Islamic State group, is accused of opening fire on June 25, 2022 outside two bars in central Oslo, including a famous gay club, just hours before the Pride Parade.
Nine other people were wounded.
Norway's public prosecutor has sought the maximum penalty of 30 years behind bars -- with possible extensions -- for the 45-year-old Norwegian of Iranian origin.
Matapour's verdict is expected around 1:00 pm (1100 GMT).
He is accused of an "aggravated act of terror".
Matapour, who was restrained by passersby after the shooting, has never revealed his motives. He has pleaded not guilty.
Psychiatric experts have been divided over his mental health, and thereby his legal responsibility, as the accused has previously been diagnosed with paranoid schizophrenia.
But the public prosecutor considered him criminally responsible and said that he deliberately targeted the LGBTQ community.
During the trial, Matapour's lawyer accused an undercover agent with Norway's domestic security service of provoking the attack by encouraging his client to pledge allegiance to IS.
He pleaded for his client to be declared criminally irresponsible, which would lead to his mandatory transfer to a secure psychiatric hospital.
In June 2023, the intelligence agency apologised after a report it commissioned, with the chief of police concluding it could have prevented the attack.
On May 3, Pakistan extradited the suspected mastermind -- Arfan Bhatti, a 46-year-old who lived in Norway.
Bhatti left Norway for Pakistan before Matapour carried out the shooting.
Bhatti, an alleged "accomplice to an aggravated act of terror", has denied any involvement and opposed his extradition.
He will be tried at a later date.
Oslo's Pride festival, scheduled to take place a few hours after the shooting, was eventually cancelled.
