John Raven was born on 13 December 1914 in Cambridge, the son of Charles Earle Raven, sometime Regius Professor of Divinity at Cambridge and Master of Christ's College, Cambridge and of Margaret Wollaston. His mother's family endowed Raven with a distinguished intellectual pedigree, including between 1723 and 1829 seven Fellows of the Royal Society (inter alios Charlton Wollaston, Francis Wollaston (1694-1774), Francis Wollaston (1762-1823), George Wollaston and William Hyde Wollaston); Raven was also a 7th generation direct descendent of William Wollaston, the philosophical writer. On his father's side, he was related to Dean Hole.
Raven was educated at St. Ronan's School, then situated at Worthing, before proceeding in September 1928 with a scholarship to Marlborough College, where he distinguished himself academically, winning prizes in English verse, Greek iambics, Greek and Latin prose and Latin verse, culminating in a scholarship to Trinity College, Cambridge. He did not confine himself to the intellectual, playing in the first XV at rugby and setting new school records in 1934 for the high jump and 440 yards.
Following the award of a first class degree in classics at Trinity Raven became in 1946 a research fellow there. In October 1948 he was elected a fellow of King's College, Cambridge, a position he held until his retirement in 1984.
During the Second World War he was a conscientious objector, basing his case on arguments by Plato. He was assigned unsalaried social work for Guy Clutton-Brock at Oxford House in Bethnal Green.
As a classical scholar, Raven's interests were in ancient philosophy. In 1957 he published with Geoffrey Kirk The Pre-Socratic philosophers, a standard work for undergraduates still in use today. Raven contributed the chapters relating to the Italian tradition (Pythagoras of Samos, Alcmaeon of Croton, Pre-Parmenidean Pythagoreanism, Parmenides of Elea, Zeno of Elea, Melissus of Samos, Philolaus of Croton and Eurytus of Croton) and on Anaxagoras and Archelaus.
While Raven's principal professional occupation was his career as a classical scholar, he applied a similar intellectual rigour to his amateur interest in botany.
From the mid 1930s John Heslop-Harrison, Professor of Botany at King's College, Newcastle-upon-Tyne, had reported significant new plant discoveries on expeditions to the Inner and Outer Hebrides. The sheer scale of the discoveries aroused scepticism and in 1948 Raven secured a grant from Trinity College to fund a trip to Harris and Rùm in July and August of that year to investigate the claims of Heslop-Harrison.
Raven's conclusions about two of the notable species were published, briefly, in Nature. He suggested that both Carex bicolor and Polycarpon tetraphyllum were introductions to Rùm, but did not comment on the possible means of introduction. His full report of the expedition and fraud was deposited in the library of King's College, Cambridge and only published in full in 1999 after the deaths of both Heslop-Harrison, his son Jack Heslop-Harrison and Raven himself. In the report Raven alleged that at some time in the 1940s Heslop Harrison transported alien plants to the Isle of Rum and planted them in the soil; he then "discovered" the plants, claimed they were indigenous to the area and that he was the first to find them. Raven's report to the council of Trinity College states: "In the interests not only of truth but also of the reputation of British science it is essential somehow to discover what plants and what insects he (Heslop Harrison) has either completely fabricated or else deliberately introduced into the Hebrides." 
Raven's classical and botanical interests were brought together in four J. H. Gray Lectures given at Cambridge in 1976, published after his death as Plants and Plant Lore in Ancient Greece.
He died on 5 March 1980 in Shepreth, near Cambridge, aged 65. Following his death a group of friends contributed to a collection of essays to commemorate his life, published in 1981 as John Raven by his Friends.