The two set off on cross-country skis dragging 180 kilogram (400 pound) sleds across the unforgiving landscape, which in 2016 claimed the life of Englishman Lieutenant Colonel Henry Worsley as he attempted a similar unassisted solo crossing of Antarctica.
In 1997, Norwegian polar explorer Borge Ousland completed the first solo crossing of Antarctica but he was aided by kites.
O'Brady made a decision over breakfast on Christmas to make a final 125 kilometer push to arrive on Wednesday at a marker on the Ross Ice Shelf, where Antarctica's land mass ends and sea ice over the Pacific Ocean begins. It took him 32 hours without sleep.
"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," he wrote on Instagram, where he kept daily records of the adventure.
"It always seems impossible until it's done," he wrote, quoting former South African President and anti-apartheid hero Nelson Mandela.