An employee of the residence, located on du Buisson Street, found the vicitm, a woman in her 60s, unconscious in her apartment just before 3 p.m. Thursday.
She was taken to Pierre-Boucher hospital where she was pronounced dead at 4:30 p.m., according to Longueuil police.
"We arrested a 50-year-old man on scene who is apparently her partner," said Const. Jean-Pierre Voutsinous.
"They were not living together, he was just visiting her."
No details about the victim's injuries have been released.
The man will be charged this morning with first-degree murder and is expected to appear in court in Longueuil later today.