Stephan Balliet, 28, is accused of shooting dead two people in October after he tried and failed to storm a synagogue.
He has been charged with two counts of murder and multiple counts of attempted murder.
Dressed in all black, Balliet was brought handcuffed into the courtroom by three armed guards. Unflinching and void of expression, he looked directly at the waiting cameras as he removed the face mask he was wearing because of the coronavirus pandemic.
Prosecutors say Balliet used explosives and firearms to try to gain access to the synagogue, where 52 worshippers were celebrating Yom Kippur, the holiest day in the Jewish calendar.
After failing to break through the synagogue's locked wooden door, he shot dead a female passer-by and a man in a nearby kebab shop.
He filmed the assault and livestreamed it on the internet.
The attack shocked Germany and fuelled alarm about rising right-wing extremism and anti-Jewish violence, 75 years after the end of the Nazi era.
Chancellor Angela Merkel, who attended a vigil at a Berlin synagogue after the attack, said the bloodshed in Halle showed Germany had “to do more” to protect Jews.
Prosecutors said Balliet made a “very comprehensive” confession, confirming “far-right and anti-Semitic motives”.
Balliet also published documents online that called for the killing of all Jews.
His video of the attack will be shown in court. Balliet faces an additional charge of incitement to hatred for denying the Holocaust in the footage.
The door of the Halle synagogue in June. Photo: DPA
According to a report in the Spiegel magazine, a psychological assessment of Balliet concluded that he has a complex personality disorder with elements of autism.
However, he was deemed to be aware of his actions and not exempt from criminal responsibility, the report said.
Baillet “described the fatal shots fired at his two victims in Halle without emotion” and appeared disappointed that he had failed in his attempt to enter the synagogue, psychiatrist Norbert Leygraf was cited as saying.
If convicted, Baillet could face life in prison.
The trial is being held at the district court in Magdeburg and scheduled to last until mid-October.
The synagogue's heavy wooden door still bears the bullet holes from the assault and will soon be removed and used for a communal art project.
President Frank-Walter Steinmeier, seen by many as Germany's moral compass, said in his Christmas speech last December that it was “a miracle” the door had resisted the attack, saving dozens of lives.
“It also symbolises what we stand for. Are we strong and resistant? Do we stand by each other enough?” he asked.
The Halle attack came three months after the murder of local pro-migrant politician Walter Lübcke in the western city of Kassel, allegedly by a known neo-Nazi.
The trial in that case began last month, with prosecutors claiming 46-year-old suspect Stephan Ernst was motivated by “extreme right-wing political convictions”.
In February this year, a gunman with apparent far-right beliefs killed nine people at a shisha bar and a cafe in the city of Hanau, near Frankfurt.
Interior Minister Horst Seehofer has since declared far-right extremism the “biggest security threat facing Germany”, promising a beefed-up security response.