Nemmouche, 33, is believed to be the first jihadist to return from Syria's battlefields to launch an attack on European soil.
He appeared Monday alongside Nacer Bendrer, a fellow Frenchman aged 30 who allegedly supplied the weapons. Both deny charges of "terrorist murder".
Nemmouche spoke only to confirm his identity as the hearing began at 10:30 am local time.
"Nemmouche, Mehdi, 33 years old, unemployed," he told the criminal court in Brussels before it selected a jury of eight men and four women for the trial, which opens on Thursday.
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 lasted only 82 seconds. 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 was born to a family of Algerian origin in the northern French town of Roubaix. He was arrested six days after the attack when 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.
Before the attack, Nemmouche is said to have fought in Syria as part of a jihadist faction and is also accused of acting as a jailer of kidnapped French journalists.
Investigators say he was in Syria from 2013 to 2014, where he met Najim Laachraoui, a member of the gang which went on to carry out suicide bombings in Brussels that killed 32 people in March 2016.
This same Brussels cell is also alleged to have coordinated and sent jihadists to carry out the Paris massacre of 13 November, 2015, in which 130 people were killed and hundreds more wounded.
Nemmouche’s court appearance coincided with the fourth anniversary of the Charlie Hebdo shootings that took place on 7 January, 2015.