A 23-year-old woman was unable to be saved after being found with fatal stab wounds inside a home in Wagga Wagga, in southwest NSW, about 11.45am on Saturday.
A 31-year-old man was arrested almost nine hours later at another home in the regional city and was later charged with murder, police confirmed on Sunday.
The pair were in a relationship, investigators said.
On Saturday afternoon, an elderly woman was found with stab injuries inside her unit at Sydney's Bondi Beach.
A 47-year-old man was arrested after police were called to the unit about 5.15pm.
Paramedics treated the woman, aged in her 90s, but she died at the scene.
The man was charged with domestic violence-related murder and refused bail.
Both accused killers are due to appear in court on Sunday.
Later in the same day, the body of a woman in her 70s was found at Mole River in the state's north.
Police were called to reports of a domestic violence incident in the regional district about 9.35pm.
Investigators believe a 37-year-old man entered a property and tried to steal a vehicle before assaulting the 74-year-old resident.
The younger man was arrested and police then went on to search the neighbouring property where they found the body of a woman in her 70s, who is yet to be formally identified.
Part of the house was damaged by fire, police said.
A crime scene has been established at both locations and an investigation launched with help from the homicide squad.
Police have not confirmed any charges against the arrested man.
NSW Opposition Leader Kellie Sloane said she was horrified by the three women's deaths, all of which were being treated as potentially domestic and family violence-related.
"My thoughts are with their families, friends and communities, and with the police, paramedics and neighbours who responded," she said, adding the incidents could not be treated as "background noise".
"We are failing women across our country and every level of government, and every one of us has a responsibility to act," Ms Sloane said.
An average of one woman was killed every 11 days by an intimate partner in 2024/25, according to the Australian Institute of Health and Welfare.
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