John Whitehead Greaves (21 June 1807 – 12 February 1880) was an English businessman who was instrumental in developing the slate industry in Wales.
His older sister Celina Greaves (1804–1884) married the brewer Edward Fordham Flower and a younger sister Rebecca Mary Greaves (1814–1892) became the mother of Sir Michael Henry Lakin, first of the Lakin baronets.
Once well established, in 1843 he married Ellen (1816–1887), daughter of a Suffolk landowner Gill Stedman.
Working existing slate deposits in partnership with other entrepreneurs, initially at Glynrhonwy but adding other sites, Greaves used the income this generated to prospect for new veins which he could exploit exclusively.
His slate won a Class 1 Prize Medal at the Great Exhibition of 1851 and orders flowed in, including a contract to supply Kensington Palace.