Fiennes was born in Windsor, Berkshire on 7 March 1944, four months after the death of his father, Lieutenant-Colonel Sir Ranulph Twisleton-Wykeham-Fiennes. While serving in Italy during World War II, his father stepped on a German mine, critically wounding him. Fiennes inherited his father's baronetcy, becoming the 3rd Baronet of Banbury, at his birth. After the war, his mother moved the family to South Africa, where he remained until he was 12. Fiennes then returned to England to attend Eton College. After graduating from Cadet School in 1963, Fiennes served in his father's regiment, the Royal Scots Greys, where he specialized in demolitions.
Becoming disillusioned by his British Army service, in particular his career prospects, he spent the last two years of his service seconded to the army of the Sultan of Oman. He led several raids deep into rebel-held territory on the Djebel Dhofar and was decorated for bravery by the Sultanate. After eight years' service, Fiennes relinquished his commission in 1971. Following his service, Fiennes auditioned to replace Sean Connery for the role of James Bond and got to the final group before being passed on for Roger Moore.
After his brief stint in showbiz, Fiennes began his career as an expedition leader. He led various expeditions; his most famous leading to the discovery of the lost city of Iram in Oman. The following year he became the first to cross the Antarctic continent unsupported, taking 93 days. In 2000, he attempted to walk solo and unsupported to the North Pole. The expedition failed when his sleds fell through weak ice and Fiennes was forced to pull them out by hand. He sustained severe frostbite to the tips of all the fingers on his left hand, forcing him to abandon the attempt. On returning home, his surgeon insisted the necrotic fingertips be retained for several months before amputation, to allow regrowth of the remaining healthy tissue. Impatient at the pain the dying fingertips caused, Fiennes cut them off himself with an electric fretsaw, just above where the blood and the soreness was.
Only four months after suffering from a heart attack and undergoing double heart bypass surgery, Fiennes ran seven marathons in seven days on seven continents, starting in Patagonia and ending in New York City seven days later. Fiennes continued to undertake various adventures, undertaking two unsuccessful Mt. Everest attempts before finally summiting Everest in 2009 at sixty-five years old. Fiennes continues to live the explorer lifestyle today, but when he’s not summiting mountains he’s happily at home with his wife, Louise in the United Kingdom.