The 85-year-old note was tightly rolled-up inside a glass bottle that was found when the memorial was being deconstructed.
"It was a fluke discovery," said Christchurch City Council head of vertical capital delivery Brent Smith.
"The contractor was working on dismantling the concrete core of the memorial when a big chunk of concrete broke off, revealing the glass bottle.
"If the concrete had not broken in that exact spot, we would never have found it."
However, the neck of the bottle was too narrow and the note too fragile because some moisture had seeped in.
They had to wait several weeks for the rolled-up piece of paper to dry out before they could have another go at extracting it.
When the note was finally unfurled it was clear some of it had disintegrated, but the handwritten names of five stonemasons who worked on the memorial were still visible.
The date the note was written - February 1937 - was also visible.
"The note is a bit worse for wear but it is an amazing link to the past that could easily have laid undiscovered," Smith said.
"I think what this note shows is that the original stonemasons were very proud of being part of building this memorial to the men and women who lost their lives in World War 1 and they wanted their role in the project to be remembered.
"I am delighted that 85 years on we have recovered the note they hid and can publicly acknowledge them for their skilled workmanship and the part they played in creating this cherished memorial," Smith said.
For the team of stonemasons working on the restoration and relocation of the memorial, the discovery was special.
"This discovery is a reminder of the rich history and tradition we’re helping to preserve," said Goldfield Stone stonemason Regan Shanks.
"It is humbling to be working on such an important memorial."
The Citizens’ War Memorial has been restored and relocated to a new spot in Cathedral Square, near where the Police Kiosk used to be.
The council aims to reveal the restored memorial in its new location in time for Armistice Day commemorations.
From the outside, Smith said it will look exactly as it did when first erected, but the internal structure will be newer and stronger.
A time capsule to be buried underneath the pavers in front of the restored memorial is likely to include a photo of the original stonemasons’ note, Smith said.