Sir Harley Hugh Dalrymple-Hay (1861–1940) was an engineer working on underground railways in and around London, England.

He was awarded the Telford Medal in gold by the Institution of Civil Engineers for his paper on the Waterloo and City Railway.

Harley Dalrymple-Hay was educated privately in Edinburgh and was articled as pupil to the Chief Engineer of the Midland Railway, working on the lines being built by that company in South Wales.

From there he moved on to the drawing office of the London & South Western Railway.

After World War I he was involved in an extensive programme of station reconstruction on the London Underground system, including the replacement of many lifts with escalators.