A wooden post in the background of the photo O'Brady shared on Instagram, he said, is the edge of the Ross Ice Shelf, which marked the end of his trip.
"As I pulled my sled over this invisible line, I accomplished my goal: to become the first person in history to traverse the continent of Antarctica coast to coast solo, unsupported and unaided," he wrote.
"While the last 32 hours were some of the most challenging hours of my life, they have quite honestly been some of the best moments I have ever experienced. I was locked in a deep flow state the entire time, equally focused on the end goal, while allowing my mind to recount the profound lessons of this journey."
O'Brady began his trek at the Ronne Ice Shelf, traveled from there to the South Pole, and then crossed to the Ross Ice Shelf, he said. He documented much of the trip on his Instagram page, even as he fought fierce wind storms, subzero temperatures and whiteout conditions.
To complete the trip, he needed to cross several mountainous areas and travel over miles of sastrugi, which are hard wavelike ridges in the snow and ice formed by wind.
O'Brady is not the first to attempt the trip. British explorer Henry Worsley tried a solo trek of Antarctica in 2016, but he had to be rescued 30 miles from the finish and later died of an infection. He had traveled for 71 days unaided before that point.
Worsley launched the attempt a century after Ernest Shackleton, the famed Antarctic explorer, survived a failed attempt to cross the continent.
Another explorer, Lou Rudd, began a solo trek of Antarctica without help on the same day as O'Brady did. Rudd reached the South Pole on December 13 and is about 90% done with the trip, according to a Shackleton brand webpage set up to track his expedition.