The verdict could tarnish the legacy of Williams, a reliable hit-maker who has won Grammy Awards and appears on NBC's music competition show "The Voice."
He and Thicke are "undoubtedly disappointed," said their lead attorney, Howard King.
"They're unwavering in their absolute conviction that they wrote this song independently," he said.
Thicke and Williams earned more than $7 million apiece on the song, according to testimony.
King has said a decision in favor of Gaye's heirs could have a chilling effect on musicians who try to emulate an era or another artist's sound.
Larry Iser, an intellectual property attorney who has represented numerous musicians in copyright cases, was critical of the outcome.
"Unfortunately, today's jury verdict has blurred the lines between protectable elements of a musical composition and the unprotectable musical style or groove exemplified by Marvin Gaye," Iser said. "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."
Gaye's children — Nona, Frankie and Marvin Gaye III — sued the two singers in 2013.
Thicke told jurors he didn't write "Blurred Lines," which Williams testified he crafted in about an hour in mid-2012.
Williams testified that Gaye's music was part of the soundtrack of his youth. But the seven-time Grammy winner said he didn't use any of it to create "Blurred Lines."
"Blurred Lines" has sold more than 7.3 million copies in the U.S. alone, according to Nielsen SoundScan figures. It earned a Grammy Awards nomination and netted Williams and Thicke millions of dollars.
The case was a struggle between two of music's biggest names: Williams has sold more than 100 million records worldwide during his career as a singer-producer, and Gaye performed hits such as "Sexual Healing" and "How Sweet It Is (To be Loved by You)" remain popular.
He and Thicke are "undoubtedly disappointed," said their lead attorney, Howard King.
"They're unwavering in their absolute conviction that they wrote this song independently," he said.
Thicke and Williams earned more than $7 million apiece on the song, according to testimony.
King has said a decision in favor of Gaye's heirs could have a chilling effect on musicians who try to emulate an era or another artist's sound.
Larry Iser, an intellectual property attorney who has represented numerous musicians in copyright cases, was critical of the outcome.
"Unfortunately, today's jury verdict has blurred the lines between protectable elements of a musical composition and the unprotectable musical style or groove exemplified by Marvin Gaye," Iser said. "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."
Gaye's children — Nona, Frankie and Marvin Gaye III — sued the two singers in 2013.
Thicke told jurors he didn't write "Blurred Lines," which Williams testified he crafted in about an hour in mid-2012.
Williams testified that Gaye's music was part of the soundtrack of his youth. But the seven-time Grammy winner said he didn't use any of it to create "Blurred Lines."
"Blurred Lines" has sold more than 7.3 million copies in the U.S. alone, according to Nielsen SoundScan figures. It earned a Grammy Awards nomination and netted Williams and Thicke millions of dollars.
The case was a struggle between two of music's biggest names: Williams has sold more than 100 million records worldwide during his career as a singer-producer, and Gaye performed hits such as "Sexual Healing" and "How Sweet It Is (To be Loved by You)" remain popular.