Dressed in their Union flag-themed Lycra, the siblings and their team mates were all smiles as they crossed the finish line in Annapolis, Maryland.
Race Across America, a 3,000 mile cross-country trip, saw the eight-person group cycle through 12 states in six days, ten hours and 54 minutes raising money for the British Heart Foundation and the Michael Matthews Foundation.
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James and Pippa's trip attracted much attention Stateside and fans spotted them taking a pit stop in rural Missouri on Wednesday.
Four days into the ride the group stopped off to refuel at a McDonald's restaurant where local residents snapped them tucking into some food.
Pippa, 30, and James, 27, then both posed for photographs before loading up their bikes and jumping into a waiting black vehicle, presumably headed for a nearby hotel to get some rest.
The Middleton siblings, whose elder sister is the Duchess of Cambridge, announced that they would undertake the challenge this month and on 14 June the pair joined nearly 300 other cyclists in San Diego, California for the start of the race.
Pippa Middleton named new ambassador for British Heart Foundation - and sets herself two fundraising challenges
Having now completed the race Pippa will now sell her bike on online auction site eBay to help generate more funds.
Pippa and James will show off their sporting ability again in July when they head to Istanbul to take part in the Bosphorus Cross-Continental Race Swimming Race; a 6.5 km swim across the Bosphorus Strait.