McMillan teamed up with Staffordshire-based military history research group, Chase Project to research the omission and then campaign to have Braithwaite properly remembered.
During their research they found two other mutineers - Gunner William Lewis from Scotland and Jesse Robert Short from Newcastle-Upon-Tyne - who were also excluded from the 306 stakes at the memorial.
Today (10.45am UK time), a service of dedication at the Shot at Dawn memorial will add three plaques and finally give Braithwaite, Lewis and Short their proper place in history.
"I am really pleased that the Arboretum has been so interested in my research on this issue and have been so supportive of the idea of paying tribute to the three mutineers by adding their names to the Shot at Dawn memorial," McMillan said.
Braithwaite's nephew David Braithwaite, a former Mayor of Hamilton, will attend the poignant service, along with relatives of both Lewis and Short.
"We do not eulogise Jack. He was a rascal and certainly not the greatest soldier but he did not deserve to suffer the fate he did," the 79-year-old told the Herald earlier this year.
New Zealand Defence Force brigadier Evan Williams is expected to attend today's service, which will also commemorate Englishman John Hipkin, who at the age of 14 was the youngest Prisoner of War (POW) of the Second World War.
Arboretum managing director Sarah Montgomery said that when they discovered three missing names, they "felt it was only right that they should be added".
The haunting Shot at Dawn Memorial features a statue of a blindfolded soldier standing with his hands tied behind his back, waiting to be executed by firing squad.
Behind it are the now 309 stakes with a plaque which has each dead man's name etched on.
Braithwaite, the "black sheep" of a prominent Dunedin family, was a self-titled "Bohemian journalist" and raconteur.
When the dark days of The Great War came, and his younger brother Horace was badly wounded during the Anzac landings at Gallipoli, he volunteered for the New Zealand Expeditionary Force.
After a year in the army, Braithwaite lost his lance corporal stripe for being absent without leave and twice trying to escape.
The 34-year-old was sent to a British army military prison in northern France where, on August 28, 1916, he became embroiled in a row with a boisterous Australian prisoner.
Braithwaite stuck up for his Anzac comrade, later claiming he was trying to pacify the situation, but was court-martialled for mutiny.
He was found guilty and sentenced to death.
Five New Zealanders were executed during the war, including Braithwaite, Victor Spencer, John Sweeney, Frank Hughes, and John King. The Australian Government did not allow death sentences.
