Donald Boudreault of Saguenay was drinking heavily one night in 2009 when he decided to call a designated driving service. He was waiting for it to arrive when he fell asleep behind the wheel of his Dodge Ram.
A passing driver called police and Boudreault was charged. His blood-alcohol level was three times the legal limit.
A judge acquitted him, ruling that he had no intention to drive, but he was convicted on appeal last year.
The decision Friday by the Supreme Court of Canada overturns that ruling and restores the original acquittal.
In its decision, the court said trial judges "must examine all of the relevant evidence ... including whether the accused took care to arrange an alternate plan to ensure his safe transportation home."
The court also said the judge who acquitted Boudreault "found as a fact that there was no realistic risk of danger."