Under the ruling Tuesday, the French gossip magazine Closer faces a daily fine of €10,000 ($13,100) if it fails to hand over the photos taken during the royals' vacation in southern France and cannot disseminate them any further, including on its website and tablet app.
The magazine published 14 photos of a partially clad Kate in its pages on Friday.
But if the royal family had hoped to block international publication, it was too late. Publications in Ireland and Italy already went ahead with the topless photos. Tuesday's ruling only affects Mondadori Magazines France, Closer's publisher. The publisher also faces a €2,000 ($2,600) fine.
"These snapshots which showed the intimacy of a couple, partially naked on the terrace of a private home, surrounded by a park several hundred meters from a public road, and being able to legitimately assume that they are protected from passers-by, are by nature particularly intrusive," the French ruling decreed. "(They) were thus subjected to this brutal display the moment the cover appeared."
The photos show Prince William's wife Kate relaxing at a private villa in Provence, in southern France, sometimes without her bikini top and, in one case, her suit bottom partially pulled down to apply sunscreen.
The lawyer for Mondadori failed to show up at the courthouse on Tuesday.
Maud Sobel, a lawyer for the royal couple, described it as "a wonderful decision."
"We've been vindicated," Sobel said.
The case is the first of two legal actions by the British royals. In a reflection of just how intent they are on protecting their privacy - and likely dissuading paparazzi from future ventures - St. James's Palace said family lawyers would be filing a criminal complaint.
Christopher Mesnooh, an American lawyer who works in Paris, said French law strongly protects privacy rights but tabloids have their own reasons for publication, even when they might violate the law.
"It appears to give satisfaction entirely to the royal couple," Mesnooh said of Tuesday's ruling.
But he added that the amount of money is nowhere near enough to dissuade the publication of similar photos.
"If you sell 100,000 copies, you're ahead of the game," he noted.
The ruling listed the royal couple by their full names: William Arthur Philip Louis Mountbatten-Windsor and Catherine Elizabeth Middleton.