Walter Duncan was a British painter and watercolorist.

He was born in London in 1848 to the artist Edward Duncan and Berthia née Huggins, the daughter of British marine painter William John Huggins. He studied art at the British Museum and the Heatherley School of Fine Art and served a seven-year apprenticeship at the Royal Academy of Arts. In 1874, he was elected an Associate of the Royal Watercolour Society. Proud of this distinction, he sometimes appended "A.R.W.S." to his name when he signed his works.

In 1871, he married Harriet Charlotte Florence Pigott née Condy (1846-1880), the daughter of the painter Nicholas Matthews Condy. After her death, he remarried the daughter of an officer stationed in the North-Western Provinces. This led to a two-year stay in India.

He died in 1932 in Richmond, London.