A white supremacist convicted of murdering a black man by dragging him behind a pickup truck is scheduled to be executed in Texas.

John William King, 44, one of three men convicted of the June 1998 killing of James Byrd, is to die by lethal injection at the Huntsville penitentiary later today.

Lawrence Brewer was executed in 2011 for the murder, while Shawn Berry - who cooperated with investigators - was given life in prison.

Berry testified during his trial that he and the two others were out drinking beer and driving around when he picked up Byrd and drove him to a remote country road.

The men severely beat Byrd before chaining him to the back of the truck.

Byrd was still alive while being dragged along a paved road for around 3.2km and suffered great pain before his death, a pathologist testified during King's trial.

His body was found outside a black church in the small town of Jasper, Texas.

The circumstances surrounding the killing horrified the US public.

Ten years after King's conviction, then-president Barack Obama signed a law in the name of Byrd, as well as Matthew Shepard, a young gay man murdered the same year, with the aim of strengthening the fight against hate crimes.

Barack Obama greets James Byrd's sisters in 2009
Matthew Shepard was kidnapped and left to die strapped to a fence in Wyoming in 1998

During the sentencing phase of his trial, attorneys for King argued prison violence compelled him to join with a white prison gang and cover his body with racist tattoos, with attorney H "Sonny" Cripps saying: "He wasn't a racist when he went in, he was when he came out."

But a psychiatrist for the prosecution said the viciousness of the crime "removed all doubt" that death was the appropriate punishment.

A guestbook at the funeral for James Byrd in 1998

The 1999 sentencing of King - a member of the racist group known as the Confederate Knights of America - was the first time since the 1970s that a white man was handed a death sentence in Texas for killing a black man.

His lawyers have since made repeated efforts to have his conviction overturned, but their attempts failed, with the Supreme Court refusing to examine King's case in 2018.

On Monday, the Texas Board of Pardons and Paroles unanimously refused to grant him a reprieve.

If King's execution is carried out as scheduled, it will be the fourth so far this year in the United States.

But some members of Byrd's family have opposed capital punishment for his killers, with his son Ross joining protests against Brewer's 2011 execution, CNN reported.

"You can't fight murder with murder," the channel quoted him as saying.