Chapman was born in London during the Blitz. His grandfather had achieved senior rank in the British Indian Army; his father served in the wartime Merchant Navy and his mother was a former midwifery training sister at Queen Charlotte's Hospital London, before running her own maternity nursing home in Ealing. His primary education was dysfunctional, with him going to no less than four schools. As a chorister at a local church, he auditioned to join the Westminster Abbey Choir School but failed because he had been watching trams driving around Westminster on a very smoggy evening, which clogged up his voice. Had he passed, he would have sung at Queen Elizabeth II's coronation ceremony in June 1953. Instead, his secondary education was at Bedales School whose headmaster, Hector Jacks, said that he would never pass A-Level examinations, which turned out to be true. In the school holidays he obtained work as an electrical stage hand / light board operator in West End theatre land, obtaining a prestigious NATKE union card.

On leaving school, he worked full time in the theatre, including stage management at the Belgrade Theatre Coventry. He followed this by joining the Royal Air Force where he trained as a fast jet pilot. He then worked for six years on sales and marketing at Lesney Products, during which time he went to night school at Enfield Tech (latterly part of Middlesex University) obtaining an HNC in Business Studies and a Diploma from the Chartered Institute of Marketing. This led to his being accepted as a mature student at Fitzwilliam College, University of Cambridge reading economics. At the same time he started the stage lighting and sound company, Entec. In 1968 his company established itself by providing the lighting for Cambridge May Balls, as well as performing liquid light shows for BBC Television, including a six month contact on Top of the Pops and a four part Doctor Who story, Claws of Axos in 1970/1. Chapman was a pioneer in touring lighting for rock acts and festivals, introducing techniques which are in use to this day. Pat and his crews provided lighting and sound systems for an eclectic mix of rock, heavy metal, pop and glam rock groups, including, to name some, The Carpenters, Bing Crosby, Black Sabbath, Ray Conniff, Dusty Springfield, Bob Dylan, Mud, The New Seekers, Lou Reed, Status Quo, Rod Stewart, Sweet, Ike and Tina Turner and Wings. In 1979 Chapman’s investor, the Marquee Club’s Harold Pendleton, took over Chapman’s Entec interests. He moved to Haslemere, Surrey, where he still lives, and spent the next four years consulting to a number of major entertainment multiples the like of Mecca Dancing, Rank Ballrooms, Warner Bros. and Pontins, both in the UK and overseas, advising on the equipping and installation of lighting and sound systems.

Branches of Chapman's family had lived in India from 1730 to 1930, first working for the East India Company then the British Raj. Chapman inherited their deep-rooted interest in the country, her history, her food and curry in particular. After he left school, Pat’s friends, knowing his passion for the subject, asked him to teach them the secrets of spices and their cooking. At that time little information had been published on the subject of curry, yet national interest in the subject was emerging. He decided to set up a club as the vehicle to exchange information. In 1981 Chapman's friend and writing mentor, columnist Carol Sarler, then editor of the best-selling Honey Magazine, wrote a piece on curry featuring the (then) non-existent Curry Club with recipes by Chapman, after which the Curry Club was founded on 1 January 1982.Many like-minded people have joined the Curry Club since it began and come from every continent including Asia. Membership is a cross-section of the British public.

Chapman frequently demonstrates curry, holds regular curry cookery courses and from time to time takes small groups of curry enthusiasts to India to visit a region and sample its cuisine.

Chapman sits on the Army Benevolent Fund committee, specifically to help with fund-raising for their annual Big Curry event

Chapman’s first cookery book, The Indian Restaurant Cookbook, was published in 1984 and is still in print. To date Chapman has written some 36 books, with international sales exceeding 2 million copies. Most are on Curry, but some of his other books cover cuisines such as Thai, Chinese, Middle Eastern and International spicy cuisines. His Balti Cookbook was the first on the subject and became a Sunday Times Number 1 bestseller. Food writer Rosemary Stark’s review in the Daily Mail said “Chapman is responsible for Baltifying Britain”.

Chapman built up a database on Indian restaurants, which as of 2009 contained over 9,000 entries. In 1984, this led to the publication of the Good Curry Guide, a critique of the top 1,000 UK curry restaurants. It has been sponsored by Cobra Beer since 1992, and was cited by the Oxford English Dictionary for usage of the word balti Sir David Frost said on his breakfast TV programme “it [the Guide] tells you everything you want to know about curry” and Delia Smith wrote, in the The Mail on Sunday's You Magazine “with it he [Chapman] has done the nation a real service”.

Chapman has appeared on British television many times, including on the shows Who'll Do The Pudding?, This Morning, Food and Drink, Great Food Live and Good Food Live. He also had a regular spot on the Good Morning with Anne and Nick show.