Private Charles Gage joined the 56th Battalion on December 2, 1916, but was killed by shellfire the next day as he travelled to join his unit on the front line.

His brother, a soldier with the 54th Battalion, erected a grave that did not bear Private Gage's name but did have details of his battalion.

Recently, researchers were able to identify who the grave belonged to when they determined Private Gage was the only soldier to die on December 3, 1916 who also had a brother in the 54th Battalion.

Lance Corporal Christopher Gage, Private Gage's brother, was killed during the Battle of Polygon Wood in September 1917. The pair were from Eugowra in New South Wales.

Veterans Affairs Minister Darren Chester said the brothers were two of at least 1000 indigenous Australians who served in World War I, despite restrictions around their enlistment.

"Indigenous Australians have served our nation in wars, conflicts and peacekeeping operations since the Boer War in South Africa from 1899-1902," he said.

"The deaths of the Gage brothers are symbolic of the tremendous service Aboriginal and Torres Strait Islander men and women have made in defence of our country for more than a century."

Private Gage's grave will now be marked with a headstone bearing his name and service details at his final resting place in Flers, France.

Mr Chester thanked researchers from Fallen Diggers Incorporated, who worked to put a name to the soldier.

"Private Gage is the 27th previously-unknown Australian World War I soldier the group has helped identify, bringing closure to the families of our fallen, and allowing us all to know the name and history of those who have made the ultimate sacrifice," he said.

Australian Associated Press