Travelling 14 hours a day, her gruelling 18 day trek ended triumphantly when she arrived at the South Pole at 10.40pm last night British time.
The 28-year-old children's TV presenter is the first person to use a bike as part of an expedition to the Pole.
She also travelled by ski and kite as she battled with severe snowstorms, temperatures as low as -48 degrees Celsius, numerous blisters, a hacking cough, stomach troubles and a bad bout of dehydration.
She said: "This has been a massive adventure and at times it felt like it was never going to end.
"My body hurts in so many different places, mentally I'm exhausted and I've only washed once in the last 30 days, so to be finally standing at the Pole feels incredible.
"I've seen how Sport Relief money makes a big difference and that's why I can't complain about any part of this because it's nothing compared to what some people go through every day of their lives."
During her challenge the broadcaster set a new Guinness World Records title for the fastest 100km by kite ski, travelling the distance in 7 hours and 28 minutes.
Explorer Sir Ranulph Fiennes said: "I take my hat off to Helen Skelton. I have to admit when she first told me that she was going to cycle part of the way to the South Pole, I laughed. But through pure grit and determination she has got there and shown that yes you can use a bike to reach the Pole. Her incredible efforts are a great example of willpower."
Miss Skelton has previously kayaked 2,010 miles down the Amazon River, for Sport Relief 2010, achieving two Guinness World Records in the process, and in February last year became the first person to high-wire walk between the chimneys of Battersea Power Station for Red Nose Day.
In her latest challenge she covered 329 miles by kite ski, 103 by bike, and 68 by cross country ski.
A Sport Relief spokeperson said: "She hopes her incredible efforts will inspire people around the UK to enter the Sport Relief Mile and raise money to help those living incredibly tough lives in the UK and the world's poorest countries.
"This was one of the toughest physical challenges ever undertaken in aid of Sport Relief and the public can still show their support and sponsor Helen now at http://www.sportrelief.com/helen.