Sentencing after the two-month-long jury trial over what is seen as the first attack by an Islamist militant with European citizenship after returning from Syria will be announced at a later date.
Nemmouche, 33, admitted to carrying a Kalashnikov, a revolver and ammunition similar to that used in the museum shooting. But his lawyer said his client did not pull the trigger in the attack that killed an Israeli couple and two museum staff, Belgian public broacaster RTBF said.
Nemmouche told the court he was "tricked" while his lawyer said video footage of the shooting was faked and his client was framed by hit men sent to kill two agents of Israel's Mossad - assertions that outraged the victims' families and survivors.
European Jewish Congress chief Moshe Kantor on Thursday condemned as a disgrace "the use of reprehensible tactics and conspiracy theories (of) the defence lawyers."
The shooting attack in May 2014 was the first to underscore the threat posed by radicalised Muslims returning to their home countries in Europe after fighting with Islamist factions in Syria's civil war