Mehdi Nemmouche, 33, faces a life sentence for shooting dead two Israeli tourists, a French volunteer and a Belgian receptionist at the Jewish Museum on 24 May 2014.
The jury trial at a Brussels criminal court, is expect to involve more than 100 witnesses, and could run until the end of February. Heavy security has been deployed around the courthouse, as victims’ families and Jewish leaders are attending the trial.
Nemmouche is appearing with Nacer Bendrer, another French man, who is accused of supplying the pistol and assault rifle that Nemmouche used in the attack. Both have denied the charges of "terrorist murder".
Investigators say Nemmouche and Bendrer met while in prison over ten years ago in southern France, where they were both described as inmates who were radicalised and trying to win over others.
According to investigators, Nemmouche fought with jihadists in Syria from 2013 to 2014, where he met a member of the group that carried out suicide bombings in Brussels in March 2015. The same Brussels-based cell also allegedly coordinated the 13 November 2015 Paris attacks.
Nemmouche is expected to face a separate trial in France for holding French journalists hostage in Syria. During the Brussels trial, those hostages are to testify about Nemmouche's character, though the defence has argued that the cases should stay separate.