Sheardown had Alzheimer's disease but succumbed to prostate and colon cancer Sunday night at Ottawa Regional Hospital, the Windsor Star reported.
"It was unexpected," his son Robin said Monday. "He will be sadly missed by everyone."
The elder Sheardown became involved in what became known as The Canadian Caper after protesters stormed the U.S. Embassy in Tehran on Nov. 4, 1979, and took dozens of Americans hostage.
Six Americans who evaded capture made their way to the Canadian Embassy, where Sheardown was second in command.
He and Canadian Ambassador Ken Taylor kept the six Americans in their private residences for months, despite the danger of being found out by the Iranian revolutionaries, the Canadian Broadcasting Corp. said.
Eventually, an elaborate ruse that included falsified passports and a fake movie production crew were used to get the six out of Iran, a real-life drama recounted in this year's big-screen movie "Argo."
Sheardown didn't get a mention in the movie but the city of Windsor, Ontario, declared Nov. 10, the day he welcomed Americans into his home in 1979, as John Sheardown Day.
"He was very pleased to know the city he loved finally recognized his efforts," his son said. "He was a true Canadian hero but he never took credit for anything."
"He was very light-hearted, but he never cringed from danger. And he always wanted to help other people."
Sheardown also is survived by his daughter Jackie Hunter, his son John Sheardown Jr., his wife Zena, six grandchildren and 10 great-grandchildren.