Middleton (29) will write a column for the upmarket chain's monthly magazine, Waitrose Kitchen, called "Pippa's Friday Night Feasts".
Her foray into kitchen advice comes after she released a book called "Celebrate" last year, which was a guide to entertaining through the year and built on the experience she gained working for her family's party-planning business.
The book by the sister of Britain's future queen was both praised and pilloried in equal measure but did not sell well and was quickly discounted in book stores.
William Sitwell, editor of Waitrose Kitchen, said readers would enjoy Middleton's relaxed and easy entertaining ideas.
"Pippa will be an excellent contributor to the magazine, bringing with her a wealth of experience of entertaining, gained in part from working at her family's party business," he said in a statement.
Her first column will appear in the magazine's April issue and will feature casual dining ideas and recipes.
Middleton said her column would be an "exciting opportunity to share my own passion and enthusiasm for food and entertaining and I can't wait to get started".