Emergency services were called to a home on Loder Street in the Gold Coast suburb of Biggera Waters, in Queensland, about 8pm on Sunday.
Detective acting Inspector Leia Urquhart said emergency services rushed to the property after a neighbour called triple zero.
They found 23-year-old Mallorie Jane Roberts with gunshot wounds at the home.
Det Insp Urquhart described it as ''a pretty confronting scene''.
Despite the "very best efforts" of first responders, the woman was declared dead at the scene.
Ethan Midgley, 23, was arrested at the home and charged with domestic violence-related murder and unlawful possession of weapons used to commit an indictable offence.
A friend of the victim's family, Haylee Harris, said she was heartbroken by the devastating loss of ''such a beautiful young mum''.
''Mallorie had a beautiful smile that could light up any room, she was so funny,'' she said.
''Her little son was her whole world - he's got no mother now, he's only two, so I can only imagine what he's going through.''
The boy had been staying with other family members at the time of the shooting, Det Insp Urquhart said.
Police seized a homemade, unregistered firearm allegedly used in the shooting.
The victim and the charged man, who is not the boy's father, were in a relationship and lived together at the home.
''Police have been in attendance to that address before, however all background in relation to the man and the woman forms part of our investigation,'' Det Insp Urquhart said.
The Queensland Domestic and Family Violence Alliance expressed ''deep sorrow'' over the woman's death.
''Tragedies like this are felt far beyond one household,'' Alliance chief executive Melanie Arnost said.
''It affects our communities and those who work every day to prevent this violence ... every woman has the right to live in safety.
''A young woman's life has been taken, and with it, a future full of possibility.''
Her friend ''had a kind heart, and always made people feel welcome'', Ms Harris said.
She had set up a GoFundMe page to help Ms Roberts' family and ''ease some of the financial burden and make sure they've got the support they need''.
''I want people to remember her as a loving mum, a daughter, a sister, and a friend,'' she said.
''No woman deserves this - she deserved so much more time with these people she loved, and I hope her memory lives on through the kindness and support our community is showing her and her family.''
Midgley's case was mentioned in Southport Magistrates Court and he was remanded in custody to reappear in July.
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