At issue was whether the 92-year-old mayor violated the Municipal Conflict of Interest Act when she voted and moved amendments in 2007 that could have benefited her son's company.
The company could have saved about $11 million in development fees.
During the hearing, McCallion's lawyers argued that she wasn't aware of the plans by World Class Developers (WCD) — of which her son was a principal — to build a $1.5-billion hotel and convention centre in downtown Mississauga.
Justice John Sproat, who released his ruling Friday morning, said he found that since WCD had not filed a complete site plan for the development, the company was not covered by the bylaw changes and would not have been able to save the development fees.
"On that basis alone [the] application must be dismissed," the judge wrote.
"In my opinion, a reasonable elector, apprised of all the circumstances as of the Votes, would not regard the deemed financial interest of Mayor McCallion as likely to have influenced her vote."
Sproat said the chances WCD would benefit from the bylaw changes were "minuscule."
Mayor's actions contrary to 'common sense'
Under examination, McCallion repeatedly said she couldn't recall details of meetings she had with WCD executives in the run-up to the votes.
The judge did criticize McCallion for putting herself in the position of possible conflict. He said her decision to participate in the votes, after reaching her own decision that she was not in conflict, was "contrary to common sense.
"Further," he writes, "Mayor McCallion was wilfully blind to the status of the WCD development."
Despite the errors in judgment, Sproat ruled that the complainant, Elias Hazineh, had not told the truth in court about when he found out about the apparent conflict.
The rules say a complaint must be filed within six weeks of the applicant finding out about the conflict.
Hazineh, a Mississauga resident, said he found out about the votes in 2011 and commenced his legal challenge within the prescribed time period. But Sproat said evidence presented in court convinced him Hazineh had found out about the conflict in 2010.
"The application," Sproat wrote, "is therefore dismissed."
At a mid-morning news conference in response to the judge's findings McCallion said, "I have no regrets."
McCallion's lawyers had argued that even if she were found to be in a conflict, she not be removed from office because her actions were not irresponsible, but inadvertent.
That's what happened in 1982 when she was found guilty on a previous conflict of interest allegation. She was found to have breached the act by voting on an issue that could have benefited her family. However, she was allowed to remain as mayor. with the judge ruling her actions were an error in judgment.
McCallion also said that her court victory would not change her mind that this will be her last term as mayor. "I'm not seeking re-election," she said.
McCallion, known across the country by her nickname Hurricane Hazel, has been mayor of Mississauga, just west of Toronto, since 1978.