The incident happened just before 1 p.m. on the 2700 block of N. Broad Street on the southbound side of the North Philadelphia station on the Broad Street Line.
Police say a 34-year-old man was shot twice in the right thigh after an argument started between the victim and a woman.
That's when police say another person got involved and shot the man twice.
Officials say the shooting happened in front of a police officer.
The victim was transported to Temple University Hospital and is listed in critical condition.
Officials confirm an arrest has been made and a weapon has been recovered.
SEPTA trains are presently bypassing the North Philadelphia station until further notice.