David Hay (10 April 1859 – 30 October 1938) was a British civil engineer of the late 19th and early 20th centuries, particularly associated with design of bridges and tunnels.

[1][2] He worked initially as a pupil of his father and was subsequently appointed as contractor's engineer on the construction of the Great Northern and London and North Western Railway joint line from Newark to Tilton and Leicester.

During 1884 and 1885 he worked on a new dock at Silloth, near Carlisle, before spending three years on widening North Eastern Railway lines in and near Newcastle-upon-Tyne.

[1] He then became a protégé of Sir Benjamin Baker, working with him on the first Blackwall Tunnel in the 1890s,[3] about which he wrote a paper with Maurice Fitzmaurice published by the Institution of Civil Engineers in 1897.

[3] Mott and Hay were internationally recognised as authorities on underground railways, being invited to write a 1905 paper for the American Society of Civil Engineers.