CBC is livestreaming reaction from outside the Guelph court.
Judge Gary Hearn said he is "fully satisfied" Sona at least aided or abetted those involved in what has become known as the robocalls scandal, though he added he believes Sona had help from one or more people.
The judge found Sona, the only person charged in the case, guilty of one charge under the Elections Act.
It is illegal under the act to interfere with a voter's right to cast a ballot.
The calls, which went out to 6,000 voters in the southern Ontario city, were linked to a disposable cellphone registered under the pseudonym Pierre Poutine.
The Conservative Party maintains that they ran a "clean and ethical" campaign and was not involved in this plot.
"Voter suppression is extremely serious and those responsible should be prosecuted to the full extent of the law. That's why we reached out to Elections Canada when we heard of wrongdoing in Guelph and did all we could to assist them," Conservative Party spokesman Cory Hann said in a statement after the verdict.
"We spend our campaigns identifying supporters and working hard to get them out to vote."
Justice Minister Peter MacKay declined to comment on the verdict.
"I really have nothing to add. There was an individual who was identified, charged, brought before the courts, there's really not much more I can say as Attorney General," he said.
Sona had been under suspicion since his name surfaced soon after the first media reports surrounding the probe, though investigators didn't zero in on him until later.
Sona worked for the Conservative candidate in Guelph at the time of the calls. The Conservative Party won the 2011 election, but Liberal incumbent Frank Valeriote held on to his Guelph seat.
Thursday's verdict does not necessarily mean the case is over, as Elections Canada's probe into the calls is still ongoing.