The sporty younger sister of the Duchess of Cambridge née Kate Middleton will take part in the Race Across America event for charity on Saturday.
Pippa, 30, and James, 27, will be a part of an eight-person team making the 3,000-mile journey from Oceanside, California to Annapolis in Maryland.
They are taking on the physical challenge in memory of their team-mate James Matthews' late brother Michael, who died in 1999 during a descent from Everest.
It is not the first time that Pippa has tested her endurance; she completed a 56-mile cross-country skiing race in Sweden in March 2012, and the previous year took part in the Highland Cross Challenge, running and cycling 50 miles coast-to-coast.
Her other interests include sailing and swimming; and she is an avid tennis fan, a regular spectator at tournaments including Wimbledon and The French Open.