Walter Mackersie Smith (1842–1906) was a British engineer who made an important contribution to the development of the compound steam locomotive.
One of his sons, Samuel Walter Johnson Smith, became a Fellow of the Royal Society.
In 1874, Smith became locomotive, carriage and wagon superintendent for the Imperial Government Railways of Japan.
He returned to Britain in 1883 and joined the North Eastern Railway where he eventually became chief draughtsman.
Smith's main contributions to locomotive design concerned the use of piston valves and compounding.