The accident happened around 10:30 p.m. at 23rd and Venango Streets in the city's Tioga-Nicetown section.
SEPTA officials say a Route R bus was pulling away from a stop when a man, who was running in an attempt to catch the bus, got his legs got caught underneath the wheels.
The victim was taken to Temple University Hospital with critical injuries.
SEPTA officials say the driver was not at fault.
The incident is under investigation.