A jury awarded Marvin Gaye's children nearly $7.4 million US Tuesday after determining singers Robin Thicke and Pharrell Williams copied their father's music to create Blurred Lines, the biggest hit song of 2013.

Marvin Gaye's daughter Nona Gaye wept as the verdict was being read and was hugged by her attorney, Richard Busch.

"Right now, I feel free," Nona Gaye said after the verdict. "Free from ... Pharrell Williams and Robin Thicke's chains and what they tried to keep on us and the lies that were told."

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 favour 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."

The Gayes' lawyer branded Williams and Thicke liars who went beyond trying to emulate the sound of Gaye's late-1970s music and copied the R&B legend's hit Got to Give It Up outright.

Blurred Lines-Song Dispute

Pharrell Williams told jurors that Marvin 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. (Nick Ut/Associated Press)

"They fought this fight despite every odd being against them," Busch said of the Gaye family outside court. Thicke told jurors he didn't write Blurred Lines, which Williams testified he crafted in about an hour in mid-2012.

Williams told jurors 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.

Gaye's children — Nona, Frankie and Marvin Gaye III — sued the singers in 2013 and were present when the verdict was read.

Sold more than 7.3 million copies in U.S.

The verdict may face years of appeals.

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.

Blurred Lines-Song Dispute

Marvin Gaye's daughter, Nona Gaye, left, and his ex-wife, Janis Hunter, take questions from the media outside Los Angeles U.S. District Court, after the judgement. (Nick Ut/The Associated Press)

During closing arguments, Busch accused Thicke and Williams of lying about how the song was created. He told jurors they could award Gaye's children millions of dollars if they determined the copyright to Got to Give It Up was infringed.

Howard King, lead attorney for Williams and Thicke, told the panel that a verdict in favour of the Gaye family would have a chilling effect on musicians who were trying to recreate a genre or homage to another artist's sound.

King denied there were any substantial similarities between Blurred Lines and the sheet music Gaye submitted to obtain copyright protection.

Williams, 41, also signed a document stating he didn't use any other artists' work in the music and would be responsible if a successful copyright claim was raised.

Thicke says wasn't present when song written

Thicke testified he wasn't present when the song was written, despite receiving credit.

The trial focused on detailed analyses of chords and notes in both Blurred Lines and Got to Give It Up

Jurors repeatedly heard the upbeat song Blurred Lines and saw snippets of its music video, but Gaye's music was represented during the trial in a less polished form. Jurors did not hear Got to Give It Up as Gaye recorded it, but rather a version created based solely on sheet music submitted to gain copyright protection.

That version lacked many of the elements — including Gaye's voice — that helped make the song a hit in 1977. Busch derisively called the version used in court a "Frankenstein-like monster" that didn't accurately represent Gaye's work.

An expert for the Gaye family said there were eight distinct elements from Got to Give It Up that were used in Blurred Lines, but an expert for Williams and Thicke denied those similarities existed.