The explorer was left bloodied and confused after his Jaguar collided with another car in Stockport, England. The other motorist spent a month in intensive care with numerous injuries.
Fiennes, who represented himself in court on Wednesday (08Sep10), admitted he must have momentarily fallen asleep before the accident.
He told the judge, ""I plead guilty. I hugely regret the incident... I travel 40,000 to 45,000 miles a year and it has not happened (before).
""There is no reason why I should have (fallen asleep) when this strange thing happened. I assumed that must have been the case.""
The 66 year old, cousin of actors Ralph and Joseph Fiennes, admitted careless driving and was fined $1,500 (£1,000). He also received four penalty points on his licence.