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The younger sister of Prince William's wife Catherine, Pippa, 29, will compete in the Speight's Coast to Coast multi-discipline event, due to start on February 8 at Kumara Beach on the West Coast of the South Island.
The party planner and author has spoken of the upcoming challenge in a column she penned for British magazine The Spectator.
"It may sound dauntingly hearty but really it's just good fun, plus it provides some routine, discipline and fitness," Pippa wrote of her preparations for the triathlon-like event.
"I'd better hold back on the food and drink, starting now."
No stranger to an outdoor contest, Pippa's recent adventures include climbing Mont Blanc, sailing the Atlantic and competing in the world's longest cross-country ski race in Sweden, according to Britain's Daily Telegraph.
The NZ event is held over one or two days with competitors cycling 140km in three stages, running 36km and and kayaking 67km as they traverse rugged conditions to reach Sumner Beach on the Pacific Ocean.
Pippa shot to fame after being watched by the world as the Duchess of Cambridge's bridesmaid at the April, 2011 Westminster Abbey royal wedding.
Her first book, Celebrate, a basic party planning guide, has been widely panned for its simplicity and has recorded struggling sales.
Among its tips is advice for the organisers of Christmas parties: "choose if you can, a Christmas-themed menu. A turkey, for example, can be perfect for large gatherings".
In The Spectator, Pippa admitted she has been "much teased" over the hardcover.
"But in my defence, let me say this: Celebrate is meant to be a guide to party planning and, as such, it has to cover the basics. If I were to write a cookery book, for instance, I would be compelled to say that to make an omelette you have to break at least one egg."