United States President Joe Biden's son Hunter pleaded guilty in a tax evasion trial on Thursday, without reaching the deal he had sought with prosecutors.

The 54-year-old admitted nine counts related to failing to pay $1.4 million in taxes over the past decade, money that prosecutors said he splurged instead on luxury living, sex workers and a drug habit.

The pleas came on the day jury selection for a trial had been due to start, and hours after Biden had offered to plead guilty in the hope of striking a deal that might keep him out of prison.

But no deal materialised and Biden made the pleas in open court.

US District Judge Mark Scarsi set sentencing for December 16. Hunter faces up to 17 years in prison and a fine in excess of $1 million.

A trial had been expected to re-hash sordid details of a life that the defendant and his family — including the president — have long acknowledged had gone off the rails.

"I will not subject my family to more pain, more invasions of privacy and needless embarrassment," US media reported Hunter saying in a statement. "Prosecutors were focused not on justice but on dehumanising me for my actions during my addiction."

Hunter has already spent a chunk of 2024 in court, having been convicted in Delaware of lying about his drug use when he bought a gun — an act that is a felony.

He has yet to be sentenced for that crime, and could face up to 25 years imprisonment.

President Biden has the power to pardon his son, but has said he would not do so.

White House Press Secretary Karine Jean-Pierre told reporters Thursday that his position had not changed.

"It is still very much a 'no'," she said.

Lawyers for Hunter have said he was only being brought before the court because of who he is.

"They want to slime him because that is the whole purpose," Biden's attorney Mark Geragos reportedly said during an August hearing in which he accused prosecutors of attempted character assassination.

Hunter's defence team has argued that the non-payment of taxes was an oversight in a life wrought chaotic by a spiraling drug addiction and the trauma of losing his older brother, Beau, to a brain tumor in 2015.

He has paid the back taxes, as well as penalties levied by authorities, and had previously reached a plea deal that would have kept him out of jail.

That agreement fell apart at the last minute, and Hunter is understood to have been trying to reach another since then.

That has been difficult for prosecutors, whose every move in this election year is being scrutinised by Republicans, who charge the defendant is being treated leniently because he is the president's son.

Hunter has for years been a foil for his father's political opponents, who have sought — without producing evidence — to smear the family as a group of criminals who have gained wealth and power because of Joe Biden's career.