An eight-person jury determined Tuesday that Williams and Thicke copied elements of Gaye's 1977 hit "Got to Give It Up" and ordered the pair to pay nearly $7.4 million to the late R&B legend's three children.
Millions more in potential future profits for "Blurred Lines" are now also at stake.
The Gaye family will seek an injunction against the song, which will give them leverage to negotiate for royalties and other concessions such as songwriting credit, although Tuesday's verdict could face years of appeals.
While the verdict affects Thicke and Williams' finances in the short term, artists and music industry lawyers will likely face new constraints as they sort through the verdict and its implications.
Howard King, lead attorney for Thicke and Williams, said in closing arguments that a verdict for the Gaye family would have a chilling effect on musicians trying to evoke an era or create an homage to the sound of earlier artists. Williams contended during the trial that he was only trying to mimic the "feel" of Gaye's late 1970s music but insisted he did not use elements of his idol's work.
"Today's successful verdict, with the odds more than stacked against the Marvin Gaye estate, could redefine what copyright infringement means for recording artists," said Glen Rothstein, an intellectual property attorney.
He said the decision sets a precedent because "paying homage to musical influences was an acceptable, and indeed commonplace way of conducting business and even showing respect for one's musical idols, (but) after today, doubt has been cast on where the line will be drawn for copyright infringement purposes."
Music copyright trials are rare, but allegations that a song copies another artist's work are common. Singers Sam Smith and Tom Petty recently reached an agreement that conferred songwriting credit to Petty on Smith's song, "Stay With Me," which resembled Petty's hit "I Won't Back Down."
In the "Blurred Lines" case, the Gaye family will seek an injunction against the song, giving them leverage to negotiate for royalties and other concessions such as songwriting credits.
Nona Gaye, the late singer's daughter, wept as the verdict was read and later told reporters: "Right now, I feel free. Free from ... Pharrell Williams' and Robin Thicke's chains and what they tried to keep on us and the lies that were told."
Larry Iser, an intellectual property lawyer who has represented numerous musicians such as Jackson Browne and David Byrne in music copyright cases, criticized the verdict.
"Although Gaye was the Prince of Soul, he didn't own a copyright to the genre, and Thicke and Williams' homage to the feel of Marvin Gaye is not infringing," Iser said.
King, the pair's lawyer, said record labels are going to become more reluctant to release music that's similar to other works — an assertion disputed by Richard Busch, the lead attorney for the Gaye family.
"While Mr. Williams' lawyer suggested in his closing argument that the world would come to an end, and music would cease to exist if they were found liable, I still see the sun shining," Busch said. "The music industry will go on."
So, too, will Williams' career, said Joe Levy, editor-at-large at Billboard.
"For Pharrell, the story moves on," he said. "It will move on quickly."
Williams, 41, is a seven-time Grammy Award winner whose songs he's performed or produced have sold more than 100 million copies worldwide. His hit "Happy" has helped make him a household name, as has his work as a judge on NBC's music competition show, "The Voice."
"It's much to Pharrell's advantage that he is at a high point in his career," Levy said.
Thicke's career may have more issues as a result of Tuesday's verdict — which came on his 38th birthday — because "Blurred Lines" was a global hit and his follow-up effort failed to connect with audiences, Levy said. Despite the song's popularity, feminists have criticized it, saying it promotes rape culture.
While the verdict will likely make musicians and record labels more cautious, it won't stop artists from using others' works as inspiration, Levy said.
Despite the decision, he predicted that "Blurred Lines" will continue to make plenty of money for Williams, Thicke and, in all likelihood, the Gaye family.
"People aren't going to stop playing it," Levy said. "It's not just going to disappear."
Anthony McCartney can be reached at http://twitter.com/mccartneyAPSuggest a correction