The diary of Edwin Henry Need, A Soldier on the Somme, is a rare window into the conflict that shook the world nearly a century ago.

It is an authentic voice describing three years spent on the front line of battle.

Edwin Henry Need left Australia for the Great War in 1916 and returned in 1919.

Mrs Scott knew her uncle well but said he never spoke of his wartime experiences and most relatives didn't even know about his diary until recently.

"I think it's a very precious little account and it's quite rare because he was a private. Most things written about World War I were by officers or journalists," Mrs Scott said.

Mrs Scott said her uncle's in-depth descriptions of what he saw showed he was an "intelligent observer".

He wrote of dried meat and biscuits that were the food staples for soldiers in the trenches and of the devastating effects of war on the French countryside.

"There wasn't a leaf left on a tree, there were so many shells and ammunition in the air that the trees were all stripped of leaves," Mrs Scott said.

"And huge holes in the ground from explosions as big as you could put a house in."

She said her uncle was "profoundly affected" by the horrors that he had witnessed. "They used to call it shell-shock then."

She said one of the diary's most moving passages were about camaraderie between soldiers.

"It was the greatest thing in their lives, they depended on each other," Mrs Scott said.

"It was very important and he missed that when he came back to live in the competitive, business world."

As a high school teacher, Mrs Scott said she had used the diary as a teaching tool for senior students.

"I just read little excerpts out of it and they were always quite interested."

The diary will be available to the public this Sunday in Castlemaine at the Uniting Church Hall at 3pm.