Four of the Supreme Court judges restored 59 of the 79 votes that a lower court judge threw out, preserving Opitz's narrow 2011 federal election victory.
Former Liberal MP Borys Wrzesnewskyj had challenged the results based on apparent voting irregularities at several polling stations on election day and an Ontario court judge ruled in his favour last May. Wrzesnewskyj lost to Opitz by 26 votes.
But the Supreme Court ruled Thursday that the entitlement to vote cannot be annulled due to procedural errors and that there was a lack of evidence that most of the discarded ballots came from voters who were not qualified to vote.
Opitz immediately issued a statement thanking the court for its "carefully reasoned decision."
"As the court decision confirmed, a fair election took place, the result was clear, was then confirmed on a recount and the result has now been endorsed by the Supreme Court of Canada," the statement reads.
"Fifty-two thousand people in Etobicoke Centre followed the rules, cast their ballots and today had their democratic decision upheld," Opitz said.
Wrzesnewskyj found a silver lining, despite losing his case.
"The next federal election will be run very differently," he said. "That means we're all ahead. We've all won."
Following the ruling, Opitz received a standing ovation from the Conservative caucus before a vote in the House of Commons.
A Conservative party spokesman said the MP was leaving later in the day to participate in Canada's election observer mission to the Ukraine.
Split decision on voting irregularities
The majority of the judges has a set a high bar for anyone wanting to contest an election result due to failures in record keeping.
They made it clear that that the onus is on the applicant to have very solid proof – proof that might be difficult to establish – that anything went wrong.
On the matter of missing registration certificates, the Supreme Court found that it was up to Wrzesnewskyj to prove that they were missing and the fact they cannot be found is not sufficient evidence.
They were satisfied that the certificates could have been "misplaced" because the deputy returning officer said that she "thought" they had been completed. If that sounds vague, the majority said, it is because she was trying to recall something that happened eight months earlier.
The only irregularities the court would accept were instances where there was no voter's signature on the registration certificate. The signature is supposed to be the voter's statutory declaration that he or she is over 18 and a Canadian citizen.
However, the court did allow registration certificates where an elections official has signed instead of the voter, reasoning that the official "would not put his signature on completely filled out registration forms without being satisfied of the voters’ entitlement to vote," so 10 votes were restored.
The majority also restored the ballots that had been negated due to errors in vouching, which occurs when a voter has no ID and someone swears as to their identity. There were no errors, said the court, only errors in record keeping. Even though vouching paperwork was missing, the court found that initials were enough to prove that the person doing the vouching was a relative of the voter being vouched for.
The majority also dismissed Wrzesnewskyj's cross appeal, which centred on the fact that many voters cast their ballots in the wrong polling division.
The judges said definitively that, "Voting in the wrong polling division had no effect on the result of the election … it is not comparable to voting in the incorrect riding."
Chief justice dissented
What is surprising is that three of the judges reached an opinion that is almost diametrically opposed to the four in the majority.
Chief Justice Beverley McLachlin and Justices Louis LeBel and Morris Fish found that 65 of the 79 ballots discarded by the lower court judge should have been tossed.
The minority judges took a much harsher view of procedural errors. However, the majority leaned hard towards the entitlement of every qualified Canadian to vote.
Gavin Tighe, lawyer for Wrzesnewskyj, noted the "extremely strongly worded" dissent from minority.
"The Chief Justice, in her words, says she cannot accept the view of the majority ... (that) imperfections in the conduct of an election are inevitable. That is to say, I suppose, that imperfections are acceptable. I don't think that is the kind of elections Canadians want," Tighe said after the ruling.
The daunting logistics of running a federal election seemed to influence the majority judges.
"A federal election is only possible with the work of tens of thousands of Canadians who are hired across the country for a period of a few days, or, in many cases, a single 14-hour day," they wrote.
There will always be irregularities, was the conclusion.
The court also found that "annulling an election would disenfranchise not only the persons whose votes were disqualified, but every elector who voted in the riding."
In a statement, interim Liberal Leader Bob Rae thanked Wrzesnewskyj for his "dedication to upholding the integrity of Canada’s electoral system," calling his faith in democracy "nothing short of remarkable."
"In addition to the split ruling today, there still exists a disturbing trend of irregularities and reports of election fraud stemming from the 2011 general election," Rae said in the statement. "We cannot forget that Canadians across the country were deprived of their right to vote through a co-ordinated attack on our democracy.
"There is still much work to be done and many questions to be answered in order to restore our confidence in Canada's electoral institutions," he said.
Read Kady O'Malley's liveblog from the Supreme Court: