The 23 year-old died shortly after gardaí went to a block of flats in Mailcoach Road in the town following reports of a violent altercation at approximately 10.30am.
When they got there, officers encountered a man who was carrying a knife.
It is believed he had suffered stab wounds. He was in a distressed state and members of the Sligo Regional Support Unit were forced to Taser him.
Ms McGuinness was found in the apartment.
Both she and the man were taken to Sligo Regional Hospital for medical attention.
Ms McGuinness was declared dead shortly after 11am.
The scene was preserved for technical examination. Professor Marie Cassidy, the state pathologist, last night performed an autopsy on the woman’s remains.
Last night, gardaí confirmed a 33-year-old man had been arrested in connection with the killing and was being held at Sligo Garda Station under Section 4 of the Criminal Justice Act.
It is understood the man had heavy bandages covering head injuries when he arrived at the Garda station.
Ms McGuinness was the eldest daughter of a family from the Easkey area of west county Sligo.
Her father John Joe is a farm labourer and her mother Catherine has worked in pubs in west Sligo. It is understood Ms McGuinness worked in a local supermarket and had studied early childhood education at Ballinode College.
Local councillor Michael Clarke, who knew the family well, said: “The area is devastated by this tragedy. They are a lovely family — the salt of the earth.”
He described the victim as “a beautiful woman, just like a model”.
Ann Cawley, who lives in the area,
said she knew nothing of the incident until she spotted two ambulances and gardaí across the street.
She added: “A young couple were living there and I saw them sometimes but I never knew their names. They seemed to be a quite ordinary couple.”
Sligo town councillor Declan Bree said: “It’s mainly a settled community on that road which is one of the main routes into the centre of the town.
“It’s a very stressful event and my sympathy goes out to the family and other relatives of the dead woman.”
Friends and relatives of Ms McGuinness last night took to social media to express their shock and sadness at her violent death.
“Absolutely shocked and devastated by losing you Natalie,” wrote one. “You where [sic] one of the most bubbliest and fun loving people this world has ever meet and u will be sorely missed. Until we meet again, rest in peace”.
- Gardaí have launched a murder investigation and anyone with information can contact Sligo Garda Station on 071 9157000.