The unveiling is being organised by Dr Lynley Hood, of Dunedin, who said the commemorations would "lift the great dark cloud around Minnie Dean by treating her with dignity and respect".
The headstone was commissioned by Dean's great-great nephew, Martin McCrae of Stirling, Scotland.
It was erected on Tuesday, replacing an unauthorised headstone which had appeared a week earlier.
Mr McCrae will not attend the service, but he said in a telephone interview the unveiling would allow his family "to get on with life and those who have died can be put to rest".
"My hope is that the laying of the stone will indeed bring peace to my family, to all who have been affected by Williamina's [Minnie Dean] fate, and to Williamina herself and her husband Charles Dean, who is buried with her."
Dr Hood said a descendent of Dean, Paula Wells, of Timaru, would read some words on behalf of the family.
It was hoped descendents of children in her care would also attend.
Dr Hood expected a large contingent from the local community would attend the 2pm unveiling, and she believed several hundred people might attend.
The service would be led by the Rev Tekura Wilding of Winton, because Dean was a devout Presbyterian.
Julien van Mellaerts, of Dunedin, will sing Scottish folk song The Four Marys, which Dean quoted in parts in her last statement.
"It's little did my mither think the day she cradled me that I would travel sae far frae home or hang on a gallowstree," she wrote.
A bagpiper would also play at the service, and Nelson-based artist, Janice Gill, formerly of Winton, would attend as she had been commissioned to paint a picture for Mr McCrae, who would also be sent a video of the unveiling.
Dr Hood said the mood surrounding Dean had changed since the laying of the headstone, and she likened the reaction to "the day after the Berlin Wall came down".
"Everyone is accepting, and I think the mood has certainly changed."
• Minnie Dean was found guilty on June 21, 1895, of murdering one infant in her care, and she was sentenced to death.
She was hanged in Invercargill Jail on August 12, 1895.
She is the only woman to have been hanged in New Zealand.
