Mr Grant said his mother bought it in memory of her younger brother, Oscar Dyson, a World War I soldier who served with the New Zealand Expeditionary Force at Gallipoli.
He was admitted to No17 General Hospital Alexandria and was then sent back to New Zealand, he said. He said after six months Mr Dyson rejoined the battalion and was killed in action.
The painting is now displayed in the entranceway to the Auckland War Memorial Museum's library.
"I've had it ever since my mother died but wanted to do something about it before I passed on," Mr Grant said.
He said he had three children and one painting, which made it "very difficult" to bequeath, so he decided to donate it to the museum.
His family fully approved, he said.
Mr Grant said rather than keeping it hidden away, it should be available for others to see as well.
"There were a lot of deaths and a lot of families who lost their sons at Gallipoli."