Father-of-four Akhtar Javeed, 56, died defending his business in Digbeth from an armed robbery earlier this year.
Suraj Mistry, 26, was found guilty at Birmingham Crown Court of manslaughter and possession of a firearm.
Mistry, of Laundon Way, Leicester, was also convicted of plotting to commit robbery along with Lemar Wali, 19. Both men were found not guilty of murder.
The jury is still considering two firearms charges against Wali, of Osmaston Park Road, Derby.
Another man, 25-year-old Tahir Zarif, is believed to be on the run in Pakistan.
The court had heard the raid took place at the Direct Source 3 fast food distribution warehouse on the evening of 3 February.
A silver Renault Megane pulled up outside the warehouse in Rea Street in Digbeth and two armed and masked men armed with guns threatened the staff before binding their hands with cable ties.
Mr Javeed was initially shot in the leg when he refused to open the safe.
Then, in the struggle that followed, the company director was shot in the throat and chest - the latter bullet piercing his lung.
He managed to stagger out of the premises but collapsed in the street and died at hospital.
A man has been found guilty of killing a businessman who was shot dead during a botched warehouse raid in Birmingham.