Polanski was awarded $87,500 in damages, and his solicitors estimate that Vanity Fair's bill could run much more than 1.5. million pounds.
The 71-year-old director went to court in London to sue the magazine's publishers over an article in July 2002 alleging he had tried to seduce a woman in a New York restaurant while on his way to his slain wife's funeral in August 1969.
Vanity Fair conceded the article was inaccurate, saying the incident actually took place weeks after Sharon Tate's murder by followers of the Charles Manson clan, but maintained the gist of the contested passage in the article was true.
"It goes without saying that, whilst the whole episode is a sad one, I am obviously pleased with the jury's verdict today," Polanski said in a statement.
"Three years of my life have been interrupted. Three years within which I have had no choice but to relive the horrible events of August 1969, the murders of my wife, my unborn child and my friends."
Tate was eight-and-a-half months pregnant when she was killed.
Graydon Carter, editor of Vanity Fair, told reporters outside the court he found the decision "amazing".
"As a father of four children, one of them a 12-year-old daughter, I find it...outrageous that this story is considered defamatory given the fact that he cannot be here because he slept with a 13-year-old girl a quarter of a century ago."
Polanski could be extradited from Britain to the United States for his 1977 crime, but not from France, where he was born.