Writing advertising copy is the classic definition of copywriting. Advertising copywriting generates ideas based on advertising principles, then researches and creates advertising copy based on those ideas. Advertising copywriters have been employed for as long as advertising has been in existence. They write slogans, catch-phrases, magazine advertisements, TV commercials, radio commercials, Yellow page ads, flyers, brochures, website content--anything where one party is trying to sell a product or a service to another party.
Writing advertising copy is all about producing sales. An advertising copywriter needs to be extremely persuasive; the copywriter must be able to strike the right emotional chord in the reader, and do it quickly and effectively. Copywriters of advertising come in all shapes and sizes. The majority are employed by advertising or copywriting firms, but a market does exist for the freelance copywriter.
If you want to become an advertising copywriter, I recommend you take a course or two in writing advertising copy. Train yourself in the art of writing copy. There are also some excellent tips on this website regarding becoming a copywriting expert.
I highly recommend reading some outstanding books on writing advertising copy and understanding the copywriting industry:The Art of Writing Advertising: Conversations with Masters of the Craft: David Ogilvy, William Bernbach, Leo Burnett, Rosser Reeves, and George Gribbin. This book allows history's greatest advertising copywriters to freely discuss what they know best-- copywriting and creating. The classic primer for professional copywriters, it has over the years become equally prized as a hands-on idea starter for writers of every stripe from all walks of life.
Ogilvy on Advertising. A candid, comprehensive, and indispensable primer on all aspects of advertising, written by David Ogilvy, the advertiser most people recognize as the all-time wizard and master of the industry.
Advertising Copywriting. This book is a comprehensive treatment of copywriting as a career and a skill. Its 22 chapters cover copywriting from A to Z ... from headlines to body copy... from consumer ads to industrial ads... from direct mail to transit. helpful features include a copy-fitting guide, proofreading marks, and a list of commonly misspelled or misused words.
Here are some great online directories of copywriting professionals and services of advertising: