The 27-year-old, who was killed last weekend, will be laid to rest after a service in Donaghadee, Co Down.
Ms Montgomery was heavily pregnant with a son who she had named Liam Arthur.
A man appeared in court this week charged with her murder. Zak Hughes (28), of Ardglen Place, north Belfast, was remanded in custody.
Sarah Montgomery
Vigil takes place in Donaghadee for Sarah Montgomery
The service of thanksgiving will be held at Donaghadee Parish Church on Thursday at 3pm, following an earlier private family service of committal.
Ms Montgomery’s death has prompted an outpouring of grief.
On Wednesday evening, hundreds of people attended a vigil in her memory in Donaghadee.
Large crowds, some carrying flowers or candles, gathered at the town’s resource centre before walking the short distance to the Elmfield Walk home where her body was found last Saturday afternoon.
Addressing the crowd, Ainsley White described Ms Montgomery as a “mother, a sister, a granddaughter, a friend”.
She added: “To Sarah, family meant everything. Her two little girls meant absolutely everything to her.
“Sarah was the best mummy and she couldn’t wait to make her family complete with her little boy.”
She said: “I hope Sarah knew how much she was loved.
“I don’t have the words to describe Sarah as a friend, I was honoured to call her my best friend and my sister at the same time.
“She never failed to put a smile on your face. She was a girl’s girl, she had your back.”
The crowd then observed a minute’s silence before breaking into applause.
Dozens of people then queued to leave flowers at Ms Montgomery’s home.
The death of Ms Montgomery has led to renewed focus on the rate of violence against women and girls in Northern Ireland.
She was the 27th adult woman to be killed in Northern Ireland since 2020.
More to follow