Cox was born in Carlisle, Cumbria, England and brought up in Whitehaven until a nuclear accident at nearby Sellafield (the world's worst prior to Chernobyl) precipitated an abrupt family move to the North Norfolk coast. He grew up in a remote and essentially 19th century feudal village, Walcott-On-Sea where mains drainage, running water and even electricity were lacking for many years.

Educated at the Norwich School, an argument with his headmaster put university out of the question and he started work as a self-employed photographer. When the North Sea gas and oil boom occurred, Cox undertook a growing amount of large-format industrial photography. His company grew to employ 25 people and became a full-service advertising agency, with clients such as the FMC Corp., Philips Business Systems and other large regional clients. The business was sold when Cox was 29. He then moved to Manchester in 1985 to became the first chief executive of the Vegetarian Society of the United Kingdom, a post he held for six weeks.

Cox initiated a number of major changes at the Vegetarian Society including a higher public profile, an expanded membership, vigorous ongoing debates with the Meat and Livestock Commission, the establishment of the Cordon Vert The Vegetarian Society - The Cordon Vert School main index page cookery school with television personality Sarah Brown, and a new magazine. Cox’s reforms were not universally appreciated and internal disagreements brought about his resignation The Vegetarian Society - paul mccartney 2006 Press Release, whereupon he founded and edited the short-lived magazine Today’s Vegetarian (Future Publishing) and, most importantly, was introduced to Paul and Linda McCartney by Chrissie Hynde, another pop singer and prominent vegetarian.

In 1986 Cox wrote a bestselling book entitled Why You Don’t Need Meat Amazon.co.uk: You Don't Need Meat: Books: Peter Cox,Neal D. Barnard (Thorsons Publishers). It gained major public attention and won the Booksellers’ Association Award for the Best Non-Fiction Publicity Campaign of the Year. The book was essentially a polemic that presented the health, environmental and ethical reasons for a meat-free diet. An early appearance on BBC television’s “Wogan” was seen by millions of people and propelled the book to the no. 1 position on the paperback charts, selling 100,000 copies in the UK alone (it was subsequently published in the United States, France, Germany, Japan and many other countries).

Meanwhile, Linda McCartney and Cox had become friends and had agreed to write a recipe book with the aim of making meat-free recipes more mainstream and less unconventional. At the time, products such as Quorn, TVP (textured vegetable protein), VegeBurger and many other meat analog substances were just starting to become widely available. Despite the previous success of Cox’s Why You Don’t Need Meat, no publisher was initially interested in what eventually became Linda McCartney’s Home Cooking, some claiming that recipe books without meat ingredients would not sell. Finally, the newly-formed Bloomsbury Publishing published the book. The book rose to the hardback bestseller charts and sold several million copies worldwide.

The success of the book prompted Paul and Linda McCartney to consider establishing a vegetarian food company. Cox initially undertook consultancy for Paul McCartney on the company’s structure and focus, but finally refused the offer of becoming the company’s managing director, preferring to stay in the publishing world. It was at this point that he also decided to become vegan.

Cox continued to write and co-write, with his wife Peggy Brusseau, numerous books, including many bestsellers such as The Quick Cholesterol Clean Out (Century), The New Why You Don’t Need Meat, (Bloomsbury), Peter Cox’s Guide to Vegetarian Living (Bloomsbury), The Realeat Encyclopedia of Vegetarian Living (Bloomsbury), Superliving! (Vermillion), Secret Ingredients (Bantam), LifePoints (Bloomsbury), The LifePoints Diet (Bloomsbury), LifePoints for Kids (Bloomsbury), The LifePoints Counter (Bloomsbury), The LifePoints Cookbook (Bloomsbury), You Don’t Need Meat (St. Martin’s Press), several of which were serialized in British national newspapers.

Media interest in Sir Paul McCartney’s divorce from Heather Mills resulted in much speculation concerning the contents of tape recordings made by Linda McCartney and Cox during their time together. Despite reports to the contrary, Cox has denied selling them and has called most press speculation wildly inaccurate.

Cox gradually started working with authors, developing their book proposals and initially selling them through an external literary agency. This arrangement was superseded when Cox established his own agency. Clients include the worldwide bestselling children’s author Michelle Paver, US Senator Orrin Hatch, Nicholas Booth, television journalist and former MP Martin Bell OBE, science writer Brian Clegg, children’s authors Joe Donnelly, M. G. Harris and Amanda Lees, and former editor of The Sun newspaper David Yelland. Cox is now managing director of Redhammer Management, a literary agency recognized by the Association of Authors’ Agents.

Cox was an expert witness for the defence in the notorious “McLibel” trial. He was a close observer of the events of the 11th September 2001 in New York and has written about what he saw A Day To Remember | Peter Cox's Blog. He founded the internet writers’ community Litopia Litopia Writers' Colony - Home, is agent-in-residence there and currently hosts the Litopia podcast for writers Litopia Writers' Colony - Podcast.