The DJ said she could not believe she fell following a 10-second dramatic countdown at the end of the feat for Sport Relief.
Whiley had been in a perspex box outside Broadcasting House in London and was joined by a number of celebrities who popped in to support her.
Winter Olympic medallist Jenny Jones joined the DJ for the final few minutes and suggested that they sprint to the finish.
Moments before she completed her challenge tonight, Whiley said: "I have no voice left. I have no breath left."
The DJ added: "It's just been the most emotional experience, the most life-affirming experience, I've ever gone through."
But her biggest boost came as she finished her challenge, with Coldplay announcing on Twitter that they would donate £10,000 to Sport Relief for every hour Jo completed on the treadmill.
The band tweeted: "Massive respect to the incredible, indegafatible @jowhiley £10K per hour makes £260K sponsorship from us @sportrelief love coldplay."
Whiley said of the donation: "I have loved my challenge - it has had some highs and lows but has truly been one of the most amazing experiences ever, but everything was worth it for Sport Relief.
"I am blown away by Coldplay's generosity and it has made this challenge all the more sweeter."
Whiley took a tumble as she got off the treadmill, and said: "I can't believe I did 26 hours and then fell at the last minute."
Addressing a crowd which had gathered, she said: "It's been quite tough to be honest with you."
She was also joined by celebrity cook Nigella Lawson who brought her fudge and advised her on what she should have for breakfast today.
"I think it has to be a full English," she said.
Lawson got on to the treadmill beside Whiley, but said: "In heels I don't know whether it's that sensible."
The foodie said she has a treadmill at home.
"You can't eat as much as I do and not have a treadmill," she joked.
Whiley had to have her blisters lanced and her thigh taped up as she battled with aches and pains.
She had a brief break as she had her blisters treated, with broadcaster and singer Michael Ball serenading her during the process.
Ricky Wilson, Will Young and Elaine Paige are among those who have helped out. Winter Olympic gold medal winner Lizzy Yarnold, Clare Balding and Sally Gunnell have also visited and sweet treats were provided by The Great British Bake Off winner Frances Quinn.
Whiley has also been kept going by distractions such as a performance by Klaxons, and Ashleigh and Pudsey.
Her challenge was part of BBC Radio Around the World for Sport Relief, in which figures from BBC Radio are attempting to run, swim and cycle 25,000 miles which is roughly equivalent to the distance around the equator.