Beryl was born in Egham, Surrey, as one of four sisters. Her parents, Adrian S. B. Lansley and Ella Farmer-Francis, separated very early and mother moved to Reading, Berkshire with her daughters. Beryl attended Kendrick School there, but left education at fourteen and started to work in a variety of jobs. Having moved to London towards the end of war, Beryl attempted working as a model and showgirl. In 1948, she married her childhood friend John Cook, who was in the merchant navy. When he retired from the sea, they briefly ran a pub in Stoke-by-Nayland, Suffolk. Their son John was born in 1950, and in 1956, the family left to live in Southern Rhodesia (now known as Zimbabwe). They would remain in Africa for the next decade, where in 1960, Cook produced her first ever painting, Hangover.
The family returned to England in the mid-sixties and moved to East Looe, Cornwall in 1965, where Beryl focused more on her painting. They then moved to Plymouth in 1968, where they bought a guest house on the Hoe. Cook shared her time between running the guest house and producing more and more paintings. In the mid-seventies, her works caught the attention of one of their guests, who subsequently put her in touch with the management of the Plymouth Arts Centre, where her first exhibition took place in November 1975. The exhibition was a great success and resulted in a cover feature in The Sunday Times. This was followed by an exhibition at the Portal Gallery in London in 1976, where Cook continued to exhibit regularly until her death.
Cook was enjoying growing popularity and her paintings soon were in great demand. Her first book of collected arts was published by John Murray in 1978, and in 1979, a film was made for LWT's The South Bank Show, where she discussed her work with Melvyn Bragg. Cook then collaborated with such authors as Edward Lucie-Smith and Nanette Newman by providing illustrations for their books. She continued to regularly publish books of her own artworks up into the early 2000s, including Beryl Cook's New York (1985), inspired by her visit to the New York City.
In 1994, she received the Best Selling Published Artist Award from the Fine Art Trade Guild. In 1995, Beryl Cook was awarded the Order of the British Empire. She did not attend the official ceremony due to her shyness, and accepted the honour at a quieter ceremony in Plymouth the following year. Post Office reproduced one of her paintings as a first class postage stamp. In 2002, her painting The Royal Couple featured in the Golden Jubilee exhibition in London. Tiger Aspect Productions made two animated films called Bosom Pals using characters from her paintings, voiced by Dawn French, Rosemary Leach, Alison Steadman and Timothy Spall, and broadcast in February 2004. Channel 4 News produced a short film on Beryl and her work in 2005, and she was also the featured artist in BBC Two's The Culture Show in 2006.
Beryl Cook died on 28 May 2008 at her home in Plymouth. Peninsula Arts of the Plymouth University mounted a major retrospective exhibition in November that year. Two books devoted to the artist were subsequently released, Beryl Cook 1926-2008 and The World of Beryl Cook. In 2010, two of her paintings were used as part of the Rude Britannia exhibition at the Tate Britain. Beryl Cook's paintings have been acquired by the Gallery of Modern Art in Glasgow, Bristol City Museum and Art Gallery, Plymouth Art Gallery and Durham Museum.