Farhad Salah, of Brunswick Road, Burngreave, has been found guilty at Sheffield Crown Court of preparing to commit an act of terrorism.
Jurors failed to reach a verdict on his co-defendant, chip-shop owner Andy Star, who was charged with the same offence.
Prosecutors said, during a five-week trial, that Salah, 24, and Star, 32, were in the early stages of testing small improvised explosive devices when they were arrested in high-profile raids on their homes, a Sheffield community centre and a Chesterfield fish-and-chip shop in December 2017.
But Star, of Sheffield Road, Chesterfield, has always insisted that gunpowder and other items found in his flat above the chip shop were all connected to his long-standing interest in fireworks.
After 15 hours of deliberations the jury was discharged on Friday morning.
Judge Paul Watson QC told jurors they were the second panel to have tried the pair.
He said that another jury failed to reach verdicts on either defendant after a trial last year.
The court was told that Star will not face a third trial but will continue to be detained on immigration matters.
Salah is to be sentenced on July 24.