LONDON—A Canadian court has ordered British American Tobacco PLC, Philip Morris International Inc. and Japan Tobacco Inc. to pay 15.6 billion Canadian dollars ($12.5 billion) in damages to Quebec smokers after a 17-year legal battle, in the latest case to roil the global tobacco industry.

More than one million Quebecers—comprising smoking addicts and people who had become sick from smoking—were represented in class-action suits claiming tobacco companies should be held responsible for selling a harmful product and obscuring the health impact of smoking.

Imperial Tobacco Canada, a unit of British American Tobacco, was ordered to pay 10.4 billion Canadian dollars. Rothman's Benson & Hedges—a unit of Philip Morris—and JTI-Macdonald Ltd., a unit of Japan Tobacco, were also ordered to make payments. The case stretched back to 1998 and went to trial in 2012.

The judgment called on the companies to pay initial compensation of at least 1.13 billion Canadian dollars within 60 days, regardless of whether they appeal the ruling. Imperial Tobacco Canada's share is $743 million Canadian dollars.

The firms argued that Canadian smokers have had a high awareness of smoking health risks for decades, not least through health warnings on cigarette packaging.

But the plaintiffs, following one of Canada's largest class-action suits, said the companies didn't properly warn their customers of the risks and failed in their general duty not to cause injury to another person, according to the Quebec Superior Court in Montreal.

"The companies earned billions of dollars at the expense of the lungs, the throats and the general well-being of their customers," said Judge Brian Riordan.

The news hit U.K.-listed tobacco stocks. At 0957 GMT, BAT shares were down 2.5% at 3,504 pence. Shares in Imperial Tobacco, another tobacco company, were down 1.7% at 3,249 pence.

BAT said it planned to appeal. "There are strong legal grounds with which to challenge both the overall judgment and to seek a stay of the provisional execution order," said BAT.

Philip Morris and Japan Tobacco weren't immediately available for comment.

Laith Khalaf, an analyst at Hargreaves Lansdown, said the companies involved are likely to "throw the kitchen sink" at defending their case. "The wider implications of the legal battle are more significant than the billions of dollars in damages awarded to the plaintiffs in this particular instance."

Citi analyst Adam Spielman added that while tobacco companies have a solid track record on overturning rulings of this type, especially in the U.S., there is no such form in Canada.

"This is the first big ruling in Canada," said Mr. Spielman. "It is by no means certain that the industry will be as successful on appeal there as it has been in the U.S. Also, we expect the appeals process to take several years."

In February, the three largest U.S. tobacco companies—Altria Group Inc., Reynolds American Inc. and Lorillard Inc.—agreed to pay a total of $100 million to settle hundreds of federal lawsuits in Florida, following a class-action suit brought by state residents in 1994 over the health impact of smoking.

Units of those companies were charged with misleading consumers. The Florida cases, which collectively became known as the Engle lawsuits, sprang from an initial class-action lawsuit on behalf of a smoker, Howard Engle.

Still, despite the agreement, thousands of cases have also been dismissed.

Ed Ballard contributed to this article.

Write to Simon Zekaria at simon.zekaria@wsj.com

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