Sir John Benjamin Macneill FRS (1793 – 2 March 1880) was an Irish civil engineer of the 19th century, closely associated with Thomas Telford.

[2] After Telford's death in 1834 Macneill established his own consultancy, based in London and Glasgow, and turned his attention towards railways—his first projects were freight schemes in the Scottish coal and ironfields near Wishaw and Motherwell.

For example, the Dublin-Belfast railway line follows the line of the Dublin and Drogheda Railway along the coast (Macneill was knighted in 1844 following its completion) and many of its impressive original structures remain such as the 98-foot (30 m) high Boyne Viaduct near Drogheda, built 1851 to 1855, based on ideas developed by William Bindon Blood,[3] the 18-arch, 126-foot (38 m) high Craigmore Viaduct near Bessbrook, built 1849 to 1852, and the nearby Egyptian Arch.

In 1855, he helped survey part of a route for a railway line linking Europe to India, participating in an expedition to the valley of the River Euphrates.

Closer to home, however, as chief engineer of the Belfast and County Down Railway (founded in 1846), he was responsible for crossing the marshy estuary of the River Quoile (the first bridge was constructed of timber piles driven into the riverbed) to bring the line to Downpatrick in March 1859 (part of the line is still operational from the town's railway museum).

He later became blind, abandoned by his friends and pupils, reportedly surviving on a pittance earned from making matchboxes in the single room where he lodged.