Last year, Lehto had been sentenced to two years and four months in prison after a court found he was drunk and speeding on his boat before crashing into a bridge support pillar in Finland in July of 2010.
Lehto, 46, had appealed the sentence, claiming he was not steering the boat, but instead sitting in the back when the accident occurred.
The Finn, who raced in Formula 1 from 1989 and 1994, has now been cleared of all charges.
Lehto won the 24 Hours of Le Mans twice, in 1995 and 2005, and spent seven years driving in the American Le Mans Series.
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