The explorer's Jaguar collided with Louis Castaldo's car in Stockport, England in March (10).
Fiennes was left bloodied and bruised, but Castaldo, 39, spent a month in intensive care with numerous injuries.
At a court hearing earlier this month (Sep10), Fiennes admitted momentarily falling asleep before the accident, which happened just hours after he completed a gruelling 42-mile (68-kilometre) night-time endurance race.
He pleaded guilty to careless driving and was fined $1,500 (£1,000), as well as receiving four penalty points on his licence.
But Castaldo, who is still suffering with injuries from the incident, is fuming Fiennes was not forced to serve jail time - because the crash has ruined his life.
He tells Britain's The Sun, ""(I'm) very angry... Having done a marathon, he had a choice to sleep, not get behind the wheel.
""I feel awful physically and psychologically. I cannot take my children to football. It has affected our whole lives.""