Richard Adams, who has died aged 96, was the author of one of the most successful books of the 1970s. Published in 1972, Watership Down, Adams’s story about a colony of rabbits travelling across the country in search of a better home in the Berkshire Downs when their burrow is destroyed, became a cult novel, with a “crossover” readership.

Despite being published as an adult book, Watership Down won the two most distinguished children’s book prizes, the Carnegie medal and the Guardian children’s book prize, and sold more than 100,000 copies in Britain in its first year of publication. Unlike some such instant successes, Watership Down was not just a book of its time; it is now firmly established as a classic and has sold more than 50m copies worldwide.

The story of the publication of Watership Down is an example of the quirky nature of publishing. As a manuscript of more than 200,000 words, it was turned down by all of the major publishers and many of the smaller ones, before Rex Collings, a small independent company, picked it up. From the moment of publication, it was widely hailed as an exceptional title and almost instantly became a bestseller. At one point, it held the record for the highest sum paid for paperback rights. Its mass success and cult status was furthered by its subsequent adaptation in 1978 to animated cartoon film, with a soundtrack that included the hit single Bright Eyes.

The origins of Watership Down lay in stories Adams wrote down to entertain his daughters on long car journeys, based on his observation of rabbits from the train window on his daily commute to work. However, Adams himself did not categorise it as a children’s book. Once published, its evocation of the English countryside (the Downs near Adams’s home), combined with its detailed descriptions of rabbit society – much taken from RM Lockley’s The Private Life of the Rabbit (1964) – which includes a sharply observed study of leadership through the characters of Fiver, Bigwig and Hazel, made it as much a political allegory as a simple adventure story.

Son of Evelyn Adams, a country doctor, and his wife, Lilian (nee Button), Richard was born in Newbury, and brought up in Berkshire. He was educated at Bradfield college, Berkshire, and Worcester College, Oxford, where he studied history for two years until he was called up in 1940. He served in the Royal Army Service Corps in Palestine, Europe and the far east before returning to Oxford in 1946 to finish his studies. Adams then joined the civil service, where he worked in the Ministry of Housing and Local Government and in the Department of the Environment, before becoming a full-time writer in 1974 after the success of his first book.

Subsequent books followed quickly, including Shardik (1974), the story of a hunter and a giant bear, which was particularly poorly received by readers wanting more Watership Down; The Tyger Voyage (1976), a picture book in verse with illustrations by Nicola Bayley; and The Plague Dogs (1977). None had the same success as the tale about rabbits.

Adams was elected a fellow of the Royal Society of Literature in 1975 and held posts as writer in residence at both the University of Florida (1975) and Hollins University in Virginia (1976). He continued to write for both adults and children. He revisited Watership Down in Tales from Watership Down (1996) and contributed a short story to Gentle Footprints: A Collection of Animal Stories, which was published to raise funds for the Born Free Foundation in 2010, just before his 90th birthday.

For almost all his writing, Adams drew on his deep affection for the countryside and the wildlife that lives in it that was formed during his childhood. In his autobiography, The Day Gone By (1990), he describes how, as a child, he lost his heart twice, once to the River Kennet and once to the Downs, of which he writes: “I can’t remember ever to have done anything – anything at all – more delightful than walking on the crest of the Downs, looking away to the purple, heat-rimmed edge of the horizon.”

Adams was invited to become president of the Royal Society for the Prevention of Cruelty to Animals in 1980, having been a lifelong campaigner for animal welfare and an active member of the society, including taking part in a lecture tour in Canada in 1977 to drum up opposition to the hunting of baby seals. In a subsequent RSPCA members watchdog publication Adams was described as giving a stirring and inspiring speech as president elect, but his time at the RSPCA was short lived.

Already going through a turbulent time internally, as traditionalists and modernisers fought and tried to put right the £1m deficit that had accrued, the RSPCA council voted to shorten Adams’s term of office as president and he resigned in protest. He later commented angrily that senior members of the council were more interested in their own careers than in the welfare of animals.

He continued to be honoured for his work throughout his life, and was the recipient of the inaugural Whitchurch arts award in 2010, given by the Hampshire town in which he lived in later years. Earlier this year, it was announced that the BBC planned a new adaptation of Watership Down for release in 2017.

Adams married Elizabeth Acland in 1949, and they had two daughters, Juliet and Rosamond. They all survive him.

• Richard George Adams, writer, born 9 May 1920; died 24 December 2016