Officers responded to reports of a person with a gun at 40th and Chestnut streets just after 10:15 p.m. Saturday.
Upon arrival, police say they discovered a 24-year-old man suffering from a gunshot wound to his lower back.
The man was transported to the hospital, where he is listed in stable condition.
According to authorities, the victim stated he and two others were walking near the intersection when they saw a man shouting to himself.
As the man approached, he reportedly began shooting at the group unprovoked, striking the victim once before fleeing the scene.
A short time later, University of Pennsylvania Police stopped a 43-year-old man who was identified by the witness as the alleged shooter.
The suspect was taken into custody and transported to a local hospital for treatment.
A firearm was recovered at the scene.
A motive for the shooting remains unknown.
Police continue to investigate.