US President Joe Biden’s son Hunter has been charged with failing to pay federal income tax and illegally possessing a weapon and has reached an agreement with the Justice Department, according to a letter filed in US District Court in Delaware.

As part of the agreement, made public on Tuesday, Hunter Biden will plead guilty to misdemeanour tax offences and is expected to reach an agreement with prosecutors on the felony charge of illegally possessing a firearm as a drug user.

It is somewhat unusual to resolve a federal criminal case at the same time the charges are filed in court although it is not totally unheard of.

The deal ends a long-running Justice Department investigation into Mr Biden’s second son, who has acknowledged struggling with addiction following the 2015 death of his brother Beau Biden.

It also averts a trial that would have generated days or weeks or distracting headlines for a White House that has strenuously sought to keep its distance from the Justice Department.

“I know Hunter believes it is important to take responsibility for these mistakes he made during a period of turmoil and addiction in his life,” Christopher Clark, a lawyer for the younger Biden, said in a statement that it was his understanding that the five-year investigation had now been resolved.

“He looks forward to continuing his recovery and moving forward,” Mr Clark said.

The news comes as congressional Republicans pursue their own investigations into nearly every facet of Hunter Biden’s business dealings, including examining foreign payments and other aspects of his finances.

It also comes days after a 37-count indictment came down against former president Donald Trump for mishandling classified documents on his Florida estate, another case with even more dramatic political implications.

Joe Biden has also faced questions about his son’s business dealings and drug addiction.

The gun charge states that Hunter Biden possessed a handgun, a Colt Cobra 38 special, despite knowing he was a drug user for 11 days in October 2018.

The count carries a maximum sentence of up to 10 years in prison but the Justice Department says Hunter Biden has reached a pre-trial agreement on that charge.

Full details were not immediately available.

The White House had no immediate comment on the case.