You might think that the first fatal car crash would be after Karl Benz built his famous Patent Motorwagen in 1886, but the first fatal car accident is generally recognized as the death of the scientist Mary Ward in 1869. Amazingly, there might be a fatal accident decades before that.
Mary Ward's death is, as I said, generally recognized as the first victim of a fatal car accident. I mean, Jalopnik even wrote about it. The King's County Chronicle documented her death the day after it happened. Basically, she was thrown out of the vehicle as it turned a sharp corner.