According to Toronto Police Service, the woman suffered from "obvious trauma."
Police were called to the building at 220 Oak Street east late Saturday morning when the man who was eventually arrested called 911.
Officers are treating the scene, near Gerrard Street and the Don Valley Parkway, as a homicide.
The man, whose identity has not been made public, is facing a murder charge and will appear in court on Sunday.
"We extend our condolences to the family and friends of the victim, and to the residents of 220 Oak. Violence of this type is unacceptable in any community," said Ian McConachie, a media spokesman for Toronto Community Housing.
"We are assisting Toronto police with their investigation and have provided security footage to the police. Staff are in the community today, alongside city's crisis response team and local agencies, to support residents and connect them to any services they may need."
The buiding where the incident took place is a community-housing building under revitalization.
In February, a 45-year-old man was murdered at the same address and in December 2011, a 59-year-old was found dead on the building's 15th floor.