59-year-old David R. Mathias, III of Morrisville was found with what police say appeared to be a single stab wound to the neck.
Monday was his birthday, police said.
The incident unfolded before 4:30 a.m. Monday at a mobile home park in the 6200 block of Foster Drive.
Officers responded after a 911 call to find a woman lying in the street, several feet where she told them she lived.
She had been stabbed several times.
Inside her home, police found Mathias in a back corner area. He was pronounced dead at the scene.
Medics rushed the woman, whom police have not identified, to St. Mary Medical Center in critical condition.
She remains hospitalized with injuries are described as severe but non-life-threatening.
According to Falls Township Police Lt. Henry Ward, Mathias and the woman had "some kind of previous relationship together."
Investigators believe at one point the pair was a couple, that Mathias owned the home, and that they recently broke up.
The woman was able to tell police that Mathias came to the home before 4:25 a.m., that some kind of fight preceded the stabbings and that she wounded him in some way before fleeing the house, Ward said.
Neighbors told police Mathias hadn't been seen in the neighborhood for some time.
They told Action News they were shocked and saddened by word of the killings.
"They're fantastic, very friendly," said Christine Taylor. "This is really horrible."
"I'm in shock, a lot of pain," said Mick Grandinetti. "We love Dave."
Police believe this was a domestic incident involving only the couple, but they were still trying to piece together the details, including the motive.
They said it was too early to determine if this was a case of the woman defending herself again Mathias.