Cornelius Prout Newcombe (5 September 1825 – 30 July 1913) was an English educator and social reformer associated with vegetarianism, early veganism, and the temperance movement. After working in insurance and shipbuilding, he became a schoolmaster. Around 1859 he operated a vegetarian boarding school, and in 1868 he founded Alexandra Park College in Hornsey. He later worked as a head teacher in New Zealand before returning to England.

Newcombe was active in the British vegetarian movement from the late nineteenth century. He edited The Vegetarian Messenger and Health Review, published The Manifesto of Vegetarianism (1911), and argued that humans were anatomically adapted to a plant-based diet. He also promoted the claim that strict vegetarianism could cure cancer and sought funding for a Fruitarian Cancer Hospital. In temperance work, he edited the Temperance Gazette and worked with temperance organisations. After his death, the Vegetarian Society established an essay prize in his memory.

Cornelius Prout Newcombe was born on 5 September 1825 in Shoreditch, Middlesex. He was the second son of Frederick Newcombe, a butcher, and Hannah Newcombe (née Prout). He was related to the painter Samuel Prout, the musical theorist Ebenezer Prout, and the artist and suffragist Bertha Newcombe.

In the early 1850s, Newcombe became a partner in Griffiths, Newcombe & Co., an insurance brokerage and shipbuilding firm. The partnership collapsed in 1854, after which he became a schoolmaster. Around 1859, he ran a vegetarian boarding school. In 1865, he was elected a member of the Royal Society of Arts. In 1868, he founded Alexandra Park College in Hornsey. He later worked as a head teacher in New Zealand before returning to England around 1895 and retiring to Torquay.

Newcombe adopted a vegetarian diet around 1850. In 1895, he attended the autumn congress of the Vegetarian Federal Union in Birmingham.

In 1905, at the age of 80, Newcombe organised and presided over a meeting of vegetarian octogenarians in London. Speakers included Newcombe, Joseph Wallace (84), T. A. Hanson (86), John E. B. Mayor (80), Samuel Saunders (91), and Samuel Pitman (82), brother of Isaac Pitman.

Newcombe claimed that a strict vegetarian diet could cure cancer and published the pamphlet The Diet Cure of Cancer, which reached a third edition in 1905. In the pamphlet, he wrote that the adoption of vegetarianism would reduce disease and change human conduct:

not cancer alone, but the foul brood of diseases that fill the world with suffering and sorrow will rapidly decrease in number. Humanity will gain its right place among the religions of the world, the causes of war will cease, and cruelty will be known only as a crime.