The explorer wanted footage of the 2004 mountaineering trip in the Cotopaxi region of Ecuador to look good for viewers on U.S. TV network HBO.
Natalie Harrison, 38, from Dorset, England staged the stunts - including a pretend fall down a crevasse in a glacier - and was subsequently "saved" by guides holding ropes, but she suffered head and neck injuries, an appeal court was told.
Harrison sued British adventure holidays company Jagged Globe, who laid on guides for the expedition at Fiennes' request, and last year (11) a judge found the firm liable for the injuries.
However, three judges at the Court of Appeal have now exonerated the company of any responsibility for the "stunts" carried out at the star's alleged suggestion, and Harrison was handed an $80,000 (£50,000) bill for legal costs. Fiennes - third cousin of actors Joseph and Ralph Fiennes - was not a defendant.
Lord Justice Pitchford said, "Sir Ranulph suggested they should undertake a staged fall which would be captured on camera. The victim would fall into a crevasse. Miss Harrison volunteered to be the victim.
"She would jump a crevasse, fall slightly short and be held suspended on climbing ropes by the guides. During this stunt her head was propelled forward into collision with the wall of the crevasse.
"In a second staged fall, she pretended to fall while climbing. The first stunt caused long term headaches and the second caused soft tissue injury to her neck."
"Sir Ranulph Fiennes did not want to do the stunt himself, that is why she volunteered. She volunteered freely and without compulsion."