Ajitpal Singh Sekhon was sentenced to 10 years after his 2011 trial.
On appeal, Sekhon argued that he didn't know the cocaine was concealed in the truck and that the court was wrong to have allowed some expert testimony from a police officer.
In a 5-2 decision, the Supreme Court says part of the policeman's testimony was inadmissible, but that the rest of the evidence in the case was overwhelming.
Writing for the majority, Justice Michael Moldaver says the inadmissible evidence was a small part of the evidence against Sekhon, while the two dissenting justices called it a major error to have allowed it.
The only issue at trial was whether Sekhon knew about the cocaine. He testified that an acquaintance asked him to drive the truck and that he didn't know about the drugs.
The police officer testified that he had never heard of drug smugglers using a blind courier — that is, someone who wasn't aware they were carrying drugs.
The Supreme Court ruling said that testimony was irrelevant and should have been excluded. However, the majority found there was plenty of other evidence to sustain the conviction.
"The flawed testimony upon which the trial judge relied forms one sentence of a 16-page judgment that is otherwise flawless," Moldaver wrote. "In particular, the trial judge provided a long list of reasons for disbelieving the appellant and rejecting his testimony as incredible."
Chief Justice Beverley McLachlin and Justice Louis LeBel disagreed.
"The Crown’s case against the appellant was circumstantial, the errors of law were very serious, and I do not believe the evidence would inevitably have resulted in a verdict of guilt despite these errors," LeBel wrote in the dissent.
"I would order a new trial."