In its ruling, the Appeal Court said it saw no reason to interfere with the trial judge's decision against Jaroslaw Dziecielski.
"The employee's conduct in these circumstances amounted to serious misconduct despite his unblemished employment record," the Appeal Court said.
"Dismissal was appropriate in the circumstances."
Court documents show Dziecielski was a 23-year employee of Toronto-based automotive-parts company Lighting Dimensions and had become a vice-president.
On a morning in April 2007, he was on his way back from the Honda plant in Alliston, Ont., in a company pickup truck he was not authorized to be driving. Dziecielski, then 45, stopped for lunch and drank four beers in an hour.
After lunch, he lost control of the truck, which went off the road and rolled over. The pickup was all but demolished and Dziecielski came away with life-threatening injuries, including a broken neck.
He later pleaded guilty to driving drunk.
Lighting Dimensions fired him a month after the crash. It noted he had damaged the company vehicle he was driving without authorization, and cited the criminal charges against him.
Dziecielski sued for wrongful dismissal and claimed various damages.
Ontario Superior Court Justice Kevin Whitaker dismissed the claim in March last year.
Whitaker noted that firing a long-term worker with an otherwise clean record for an isolated incident is normally unwarranted.
However, the judge found Dziecielski was "certainly guilty of serious misconduct" that had attracted criminal sanction and put his company at risk of lawsuits and a damaged reputation.
"This single act of drunk driving during this long service is not just bad judgment or inadvertence," Whitaker wrote.
He awarded $28,900 in costs to the company.
In siding with Whitaker's findings, the Appeal Court said it found no reason to interfere with his ruling that, despite the long service, the company had acted appropriately in firing Dziecielski.
The court also ordered him to pay a further $11,500 in costs.