Parker Liautaud, who went to Eton College, is the youngest man to have skied to the South Pole, having completed the expedition in 18 days.
The teenage environmental campaigner has already been on three expeditions to the North Pole, the first when he was just 15.
He set off for the 349 mile (561km) trek on December 3 with two main goals: "The first was to undertake scientific research and collect data samples.
"And the second was to reignite the dialogue on climate change by creating a story that people can engage with and be a part of."
After reaching the South Pole on Christmas Eve, Mr Liautaud said: "The whole journey is really a mental one, managing uncertainty and trying to figure out how to manage risk. It is really a big relief to know that we have done it."
The previous coast-to-Pole speed record was held by Christian Eide, from Norway, who made the trip in 24 days.
Mr Liautaud undertook the expedition with his companion Doug Stoup.
"It was difficult to really not see the expedition as one big countdown to the South Pole," Mr Liautaud said. "It was important to break it up in to manageable chunks. That is really the only way to get through - take it milestone by milestone. I am very lucky to have had the opportunity to do the expedition. I feel fantastic. It could have gone either way."
On his way to the South Pole, Mr Liautaud stopped to collect snow samples and deployed a lightweight weather station to measure and transmit climate data.
He had attempted to be the youngest person to reach the North Pole aged 15, but his team evacuated 15 miles from the end of their trip. He completed an expedition to the North Pole a year later.
Mr Liautaud said he hoped to spend Christmas Day asleep, adding: "I have lost around 20lbs and I've only eaten nuts and dried food for the last month. I am really looking forward to having my first proper meal. I know it will be the best feeling waking up on Christmas Day knowing I don't have to walk another 17 miles."
Mr Liautaud is half French and half American. He is an ambassador for One Young World, an organisation for aspiring young leaders. He grew up in California, but moved to London when he was nine and went to Eton College from 13 to 18.
After completing his Bachelors degree in Geology and Geophysics at Yale University in the US, he plans to continue with scientific research and do a PhD.