It happened around 1:00 Sunday morning at T-Barr's Place on the 2200 block of South 8th Street.
Authorities received a report of someone unconscious inside the bar and arrived to find the 44-year-old bartender suffering from multiple stab wounds.
The victim, identified by friends as George Fox, was later pronounced dead.
Investigators say that surveillance video shows a man in a hoodie walked casually into the bar and demanded money from the bartender. The suspect then stabbed the victim, stole cash from the register and took off.
Sources say there were about 15 people inside who sat still - stunned by the killing they just witnessed.
"People witnessed and no one did anything - that upsets me," said Tom Barr, owner.
The victim's girlfriend of 10 years was at the scene later Sunday morning, putting out a plea for information.
"If anybody knows anything please come forward. This was a ruthless and senseless act - it should have never happened. It's going to take awhile to get over this but please anybody come forward and get justice taken care of," said Debbie Diantonio.
Diantonio says she didn't like her boyfriend working at the bar because it tends to get rowdy.
Barr told Action News that the victim stopped working there three years ago, but came to fill in for the usual bartender.
"For a couple dollars you gotta kill somebody, that's ridiculous," said Barr.
The murder is one of many violent crimes that took place overnight in Philadelphia. In all, seven people were shot, one person was stabbed - four of the victims died.
Anyone with information is asked to contact Philadelphia Police anonymously at 215-686-TIPS (8477). Tips can also be submitted via phillypolice.com or by downloading the i-Watch Philadelphia app on your smartphone.