The 68-year-old cousin of acting siblings Ralph and Joseph Fiennes will tackle -50C (-58F) temperatures next year (13) on what has been dubbed the Coldest Journey On Earth.
Fiennes hopes the six-month trek will raise over $9.6 million (£6 million) for blindness charity Seeing Is Believing.
He says, "There is a huge, blank knowledge of the winter of Antarctica, what is happening to Antarctica during a period when the scientists can't normally get out there.
"Our caboose will be bristling with scientific instruments for NASA and the European Space Agency."
The explorer already holds the record as the oldest Brit to climb Mount Everest after he reached the summit aged 65.