Shots rang out at around 2:45 p.m. on a Broad Street Line train near Fairmont Avenue in north Philadelphia's Francisville neighborhood, the department said.
The victim, a 21-year-old black man, was shot 11 times and taken to Temple University Hospital where he died from his wounds, police confirmed.
The other victim, a 16-year-old, was treated for a gunshot wound to the left arm, where his condition was listed as stable by Monday afternoon, they added.
No arrests have been made in connection with the killing, reports indicate. Philadelphia police said they were still on-scene investigating as of 5 p.m.
Click here to follow Daily Voice Bristol and receive free news updates.