Mehdi Nemmouche, the first jihadist to return from Syria's battlefields to allegedly launch an attack on European soil, faces a life sentence if convicted of the killings in the Belgian capital on May 24, 2014.
Both Nemmouche, 33, and Nacer Bendrer, a fellow Frenchman aged 30 who allegedly supplied the weapons, deny charges of "terrorist murder".
Nemmouche, wearing a blue sweater, spoke only to confirm his identity as the hearing began at 10:30 am (0930 GMT).
More than 100 witnesses are due to testify at the trial, which will be attended by the victims' families and Jewish community leaders, who have denounced the anti-Semitic nature of the attack.
And more than 300 Belgian and foreign journalists have registered to cover the proceedings which could last until the end of February.
The deadly attack, which lasted only 82 seconds, shocked Belgium and the world.
Firing a pistol and then an assault rifle, the gunman killed two Israeli tourists, a French volunteer and a Belgian receptionist at the Jewish Museum.
Nemmouche -- born to a family of Algerian origin in the northern French town of Roubaix -- was arrested six days after the attack.
He was caught in the southern French port city of Marseille after arriving on a bus from Brussels, carrying a handgun and an assault rifle.
That same Brussels cell is also alleged to have coordinated and sent jihadists to carry out the Paris massacre of November 13, 2015, in which 130 people were killed and hundreds more wounded.
Nemmouche and Bendrer, investigators say, met nearly a decade ago while in prison in southern France, where they were both described as "radicalised" inmates who tried to win others over.
Nemmouche is expected to face a separate trial in France for holding French journalists hostage in Syria.
The former hostages are expected to testify about Nemmouche's character during the Brussels trial, despite the defence arguing that theirs is a separate case.
The defence team, Benizri added, may even try to "twist" the facts by repeating "totally far-fetched" claims that Israel's intelligence service Mossad staged the attack.
Courtoy himself suggested Israeli agents could be behind the attack when he spoke at a pre-trial hearing on December 20.
While Jewish groups say the evidence against Nemmouche is "overwhelming," Courtoy argued "a trap" was sprung on his client.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)