The US Senate has voted overwhelmingly to confirm Merrick Garland, President Joe Biden’s nominee for attorney-general.

The veteran federal appellate judge won the support even of the chamber’s top Republican, Mitch McConnell, who played a key role in denying him a spot on the Supreme Court when nominated by then-president Barack Obama in 2016.

In the end, Mr Garland was confirm as the top US law enforcement official by a 70-30 vote in the Democratic-led Senate on Wednesday (US time).

Other Republicans to back his appointment included former judiciary committee chairmen Lindsey Graham and Chuck Grassley.

Mr Garland, 68, will assume the post at a time of heightened concern about domestic extremism.

He takes over a Justice Department that Republican former president Donald Trump repeatedly sought to bend to his will. The former federal prosecutor also inherits sensitive ongoing investigations, including one involving the new Democratic president’s son.

“I’m voting to confirm Judge Garland because of his long reputation as a straight-shooter and legal expert,” Mr McConnell said before the vote.

“His left-of-centre perspective has been within the legal mainstream.”

His confirmation represented some measure of vindication for Mr Garland. In 2016 the Senate, then controlled by Republicans, refused to consider his nomination to the Supreme Court by Mr Obama and declined even to give him a confirmation hearing.

By doing so, the Republicans, led by then-majority leader Mr McConnell, enabled a Republican president, Mr Trump, in 2017 to fill a Supreme Court vacancy with a conservative justice.

Mr Garland was nominated by Mr Biden to lead a department in the midst of intensive investigations into the deadly January 6 attack on the US Capitol by Trump supporters.

Mr Garland has called the attack “heinous” and promised to make the investigation among his top priorities. Hundreds of people have been arrested in connection with the incident, including members of right-wing extremist groups.

During his confirmation hearing on February 22, Mr Garland pledged to restore confidence in the department and protect it from political meddling. Mr Trump repeatedly interfered in Justice Department matters, applying pressure to go easy on his friends and allies ensnared in criminal investigations and to target political foes.

Democrats accused former attorney-general William Barr of acting on Mr Trump’s personal and political behalf rather than for the benefit of the US justice system.

-AAP