The worker, whose name has not been released, was electrocuted while tending to a downed power line in Sarnia, said the Ontario Labour Ministry, which is investigating the man's death.
It's the second fatality attributable to Sandy in Ontario — a Toronto woman died Monday night when she was hit by a sign blown down as the storm hit.
The lineman was using a bucket truck to repair fallen power lines when the incident occurred around 10 a.m., said Janice McMichael-Dennis, CEO of Bluewater Power.
McMichael-Dennis called the death an "unspeakable tragedy," adding the utility has never had a worker die on the job before.
"Our ultimate goal is to be able to support our lineman's family and... be able to see if we can work through this day of mourning," she said.
"It's a day you never want anybody to have to go through."
The Electrical Safety Authority and Sarnia police are also looking into the man's death, McMichael-Dennis said.
Sarnia Mayor Mike Bradley said the city's tight-knit community is struggling with the loss.
"It is devastating because the community was so proud of the fact that there had not been anyone injured during the storm and that we'd come through it as a family," he said.
Ontario Energy Minister Chris Bentley took to Twitter to extend his condolences to the worker's family.
"Thoughts and prayers with family of Hydro worker killed in Sarnia," Bentley wrote.
Southern Ontario was hit hard Monday and Tuesday by strong gusts of wind from Sandy. The wind warnings continued in Sarnia after they were cancelled in the rest of the province.
The region experienced winds of up to 100 kilometres per hour throughout Tuesday.
Bentley said Wednesday hydro crews have restored power to the vast majority of the 150,000 customers affected by outages as the massive weather system whipped through the province.
Outages affected another 50,000 customers in Quebec and 14,000 in Nova Scotia at the storm's peak.
In the United States, the death toll from Sandy has reached more than 60 — and more than eight million people, from Maine to the Carolinas, are still waiting for the power to return.
The Toronto Transit Commission is offering to help New York City get its subway system, which suffered the worst damage in its 108-year history, running.
Spokesman Brad Ross said the TTC could send crews to help out with structural, track or signal repairs and also offer expertise on other issues.
(The Canadian Press, AM640)
Also on HuffPost