The victim has been identified as 24-year-old Tyrik Richardson.
Richardson was shot four times inside a bathroom at Cheers Bar at 69th and Market streets early Thursday morning.
Upper Darby Police Superintendent Michael Chitwood said an argument over drugs was behind the shooting.
He also called the bar a nuisance, saying police have responded to 180 complaints at the bar in just over a year.
"This place is a shoot 'em up joint; whether it's drugs or whether it's weapons and not only do we have to make an arrest in this place, in this homicide, but we have to also see if we can't close this place down. I mean, it really, really is a criminal enterprise," Chitwood said.
Police say they have the nickname of a suspect, but have not released that information.
