In the report, released Monday, David Weiss called his prosecution of the president’s son on gun and tax crimes “impartial” and “not partisan politics”.

Hunter Biden’s lawyer said the report showed Mr Weiss’s investigation “was a cautionary tale of the abuse of prosecutorial power.”

Biden issued an official pardon for his son, who was facing sentencing for two criminal cases, in early December.

While issuing the pardon, the president said his son had been “singled out” and called his cases “a miscarriage of justice” and “raw politics”.

Mr Weiss called those statements “gratuitous and wrong”.

“I prosecuted the two cases against [Hunter] Biden because he broke the law,” he wrote in his report.

Hunter Biden pleaded guilty to tax evasion charges earlier in September, and was found guilty of being an illegal drug user in possession of a gun in June.

His father’s full and unconditional pardon for his son came after the president had repeatedly said he would not give him clemency.

It was not the first time a US president has pardoned a family member.

Bill Clinton pardoned his younger half-brother, Roger Clinton, for a 1985 cocaine-related offence in 2001.

In 2020, Donald Trump pardoned Charles Kushner, the father-in-law of his daughter, Ivanka, who pled guilty to federal charges of tax evasion and illegal campaign donation payments in 2005.

In his report, Mr Weiss acknowledged that, but added: “none have taken the occasion as an opportunity to malign the public servants at the Department of Justice based solely on false accusations”.

Hunter Biden pleaded guilty to nine counts of federal tax fraud in September, for which he had been facing up to 17 years in prison.

He was also convicted of three felonies in connection with a gun purchase in June, for which he had been facing up to 25 years in prison.

The investigations into the president’s son had resurfaced uncomfortable and embarrassing details about his personal life, including his addiction to crack-cocaine and allegedpayments to escorts.

President Biden had mostly kept quiet during the investigations into his son but came fiercely to his defence in his pardoning.

“There has been an effort to break Hunter – who has been five and a half years sober, even in the face of unrelenting attacks and selective prosecution,” President Biden said.

“In trying to break Hunter, they’ve tried to break me – and there’s no reason to believe it will stop here. Enough is enough.”

He added: “I hope Americans will understand why a father and a president would come to this decision.”

The pardon covers the period from 1 January 2014 to 1 December 2024, “including but not limited to” the tax and gun crimes for which he was found guilty.

Mr Weiss said due to that unconditional pardon, he could not make any “additional charging decisions” relating to Hunter Biden over that period.

“It would be inappropriate to discuss whether additional charges are warranted,” he said.

Mr Weiss has previously defended his inquiry into the president’s son.

In 2023, he told the House of Representatives Judiciary Committee there had never been political pressure or interference in his work from the justice department.

Mr Weiss’s investigation into Hunter Biden was heavily scrutinised on both sides of the political spectrum.

Democrats said it was politically charged and felt that Hunter Biden had an unfair target on his back.

Republicans believed the justice department was not pursuing charges aggressively enough and showing the president’s son unfair favouritism.

Hunter Biden’s guilty convictions came after a collapsed plea deal in 2023.

A judge declined to approve the deal – which Republicans had branded a “sweetheart deal” – that would have had Hunter Biden plead guilty to the tax evasion charges to avoid the more serious gun-related charges.

In a statement released Monday, Hunter Biden’s lawyer, Abbe Lowell, criticised Mr Weiss for the failed deal.

“Mr. Weiss also fails to explain why he reneged on his own agreement, a reversal that came at the 11th hour in court as he and his office faced blistering attacks from Republicans,” Mr Lowell said.

Alexander Smirnov, 44, also admitted tax evasion after not reporting more than $2m (£1.58m) in income.

His claims became the basis of an impeachment investigation in Congress which centred around the false claims that the Bidens made millions in bribes from Burisma, a Ukrainian energy company.

But Smirnov admitted he made the story up, and pleaded guilty in Los Angeles on Monday as part of an agreement with prosecutors.

Smirnov, a dual US-Israeli citizen, had been an FBI informant for more than a decade when he made the allegations about the Bidens in June 2020, saying that Joe and Hunter Biden each received $5m from the energy company.

Prosecutors said Smirnov was motivated by “bias” against President Biden and that he spun his “routine and unextraordinary business contacts” with Burisma into tales about bribery that were “fabrications”.

The FBI investigated his statements but within months recommended the case be closed without any legal action taken against the Bidens.

But the allegations refused to die, and became the basis for a Republican-led drive to investigate President Biden, including an effort to make Smirnov’s initial statement public.Prosecutors say that when he was re-interviewed by FBI agents in September 2023, Smirnov doubled down on his claims.

Smirnov was arrested in Nevada as he returned to the US from an overseas trip in February 2024.

According to court documents, he had ties with Russian intelligence and used his more than $2m in unreported income to buy a Las Vegas condominium, a lease on a Bentley car, and hundreds of thousands of dollars of clothes, jewellery and accessories.

The case was brought by Special Counsel David Weiss – who has overseen an investigation of Hunter Biden.Joe Biden issued a pardon for his son, who faced potential prison time for tax evasion and lying on a form about his drug addiction when he bought a gun.

Smirnov will be sentenced in January. The plea agreement is subject to approval by a federal judge.

He faces a maximum sentence of 35 years in prison and a $1m fine, however prosecutors and defence lawyers have agreed to a sentence of between four and six years and a restitution payment of $675,502, according to the plea deal.

In a statement, the president said his son had been “singled out” and called his cases “a miscarriage of justice”.

Hunter Biden pleaded guilty to tax charges earlier in September, and was found guilty of being an illegal drug user in possession of a gun in June – becoming the first child of a sitting president to be a convicted of a crime.

Reacting to the pardon, President-elect Donald Trump said: “Does the Pardon given by Joe to Hunter include the [6 January] Hostages, who have now been imprisoned for years? Such an abuse and miscarriage of Justice!”

Trump was referring to his supporters who stormed the US Capitol on 6 January 2021 in a bid to overturn Trump’s defeat in the 2020 election.

Joe Biden’s full and unconditional pardon for his son comes after the president had previously said he would not give him clemency.

Just a couple of months ago, in September, the White House press secretary said that Biden would not issue a pardon for his son.

But on Sunday evening, President Biden said although he believed in the justice system, “politics has infected this process and it led to a miscarriage of justice”.

“From the day I took office, I said I would not interfere with the Justice Department’s decision-making, and I kept my word even as I have watched my son being selectively, and unfairly, prosecuted,” he said.

Biden said he wrestled with the decision, and added: “once I made this decision this weekend, there was no sense in delaying it further.”

“I hope Americans will understand why a father and a President would come to this decision,” he said.

In a reaction statement, Hunter Biden said mistakes he made during the darkest days of his addiction had been “exploited to publicly humiliate and shame” his family for political sport.

“I will never take the clemency I have been given today for granted and will devote the life I have rebuilt to helping those who are still sick and suffering,” the 54-year-old added.

The younger Biden has been sober for five-and-a-half years, his father said.

This is not the first time a US president has pardoned a member of their family.Bill Clinton pardoned his younger half-brother, Roger Clinton, for a 1985 cocaine-related offence in 2001.

In 2020, Donald Trump pardoned Charles Kushner, the father-in-law of his daughter Ivanka. President-elect Trump has recently announced that Kushner will be the new ambassador to France.

Hunter Biden pleaded guilty to nine counts of federal tax fraud in September, for which he had been facing up to 17 years in prison.

He was also convicted of three felonies in connection with a gun purchase in June, for which he had been facing up to 25 years in prison.

Sentencing for these cases had been scheduled for 12 and 16 December.

His legal troubles had been a dark cloud over his father’s presidential campaign, which came to an end in July after Biden pulled out of the election race.

Biden endorsed Vice-President Kamala Harris to succeed him as the Democratic candidate, who lost the election to Republican Donald Trump in November.

Trump is set to take over the Oval Office from Biden on 20 January 2025 – Inauguration Day.