Mohammed Abdallah, whose group was linked to the Manchester Arena bomber, has been found guilty at the Old Bailey of being a member of Islamic State after his file was leaked to the media.
Mohammed Abdallah, 26, travelled to Syria with help from his wheelchair-bound brother who set up a "hub" of communication at home in Manchester, the Old Bailey was told.
He went to the war-torn country intending to meet up with three fellow jihadis, including a former RAF serviceman turned Muslim convert Stephen Gray.
While three of them managed to cross into Syria in July 2014, Gray was turned away when he reached Turkey, jurors were told.
Abdallah, who has dual Libyan nationality, allegedly went on to receive £2,000 in cash, source an AK47 assault rifle, and sign up with IS, with the assistance of his 24-year-old brother Abdalraouf.
The defendant, of Westerling Way, Moss Side, Manchester, has denied wrongdoing and told jurors he only went to Syria to help deliver cash to the poor.
He said he felt "totally deceived" and someone else must have filled out the IS form without his knowledge.