Matthew Gunn, 27, suffered catastrophic head injuries at the WM Morrisons store in Tewkesbury, Gloucestershire, in September 2014.
He had been regularly using the staircase to access his locker on the first floor of the shop when he suffered a seizure.
Mr Gunn was fatally injured, dying in hospital 12 days later having never regained consciousness.
Bradford-based Morrisons had denied three health and safety charges, but was convicted by a jury at Gloucester Crown Court. The company had admitted a fourth charge prior to the trial.
The court heard Mr Gunn died three-and-a-half months after his mother had warned managers of the risk to her son due to his frequent seizures.
Richard Atkins KC, prosecuting, told the court WM Morrisons knew of Mr Gunn’s ill-health and should have moved his locker to the ground floor and stopped him using the stairs.
“The defendant knew of the risk posed by the stairs to Matthew Gunn,” he said.
“Many in the management were aware of the frequency of the tonic-clonic seizures and the prosecution submits that by the time of the fatal failings on September 25 2014, there was a highly likely high level of harm occurring.”
The jury convicted the supermarket giant of failure to ensure the health, safety and welfare of employees; failure to carry out a suitable and sufficient assessment of the risks to the health and safety of employees; and failure to review the risks and assessments of employees.
The company admitted an offence of failing to comply between May 26 2015 and February 26 2020 with a request made by an HSE inspector for contact details of a person the inspector wanted to speak to.
Richard Matthews KC, defending, said he would address the court on the sentencing guidelines which were “cold and widely removed the human tragedy that this case concerns”.
“Nothing that I say in that cold way is intended to remove anything from that tragedy,” he said.
“The breach arose from a single incident and an isolated set of circumstances. This whole case focused on whether a locker could or should have been moved from the first floor to the ground floor.”
Passing sentence, Judge Moira Macmillan said: “Matthew was forced to use the stairs at least eight times a day for each of his breaks as he had to keep his cigarettes in his locker.
“Morrisons, as Matthew’s employers, have a duty to ensure his health and safety. The jury decided that using the stairs for the amount of times he did, was a contributory factor to his death.
“The company failed to carry out a risk assessment. Morrisons fell short of the standards expected for somebody suffering from epilepsy.
“Morrisons, in failing to move Matthew’s locker downstairs, is indisputable. The company failed to treat him as an individual and make appropriate changes. I accept that the risks were specific to Matthew.”