The incident happened before 11:30 p.m. Tuesday on the 200 block of West Main Street.
Neighbors reported hearing numerous shots fired and then screams.
Police say the victim was shot six times and collapsed near the restaurant's drive-thru window.
He was pronounced dead at the scene. His name has not been released, pending notification of family members.
The suspect fled the scene, heading towards the transportation center across the street.
Investigators were checking the restaurant's surveillance cameras for clues.
Some patrons of the busy restaurant and gas station were rattled by the homicide here at place they frequent.
"It's way too close to home cause you're not expecting nothing like this here," said Tyrone Johnson.
Other customers were not surprised to learn of deadly violence.
"It's terrible, but it's not surprising for Norristown," said Deanna Butler. "Stuff like this happens all the time."
Anyone with information was asked to call the Norristown Police Department at 610-270-0977 or the Montgomery County Detective Bureau at 610-278-3368.
Late Wednesday morning, Jonathan Chong, owner/operator of the restaurant, released the following statement:
"The security and safety of our customers and employees is always our top priority. We'd like to thank the local police department and our employees who responded swiftly and professionally."
Stay with Action News and 6abc.com for more information as it becomes available.