An American truck driver was sentenced to death on Wednesday for massacring 11 Jewish worshippers five years ago in the deadliest anti-Semitic attack in US history.

The 12-member jury unanimously ruled that Robert Bowers should be executed for the October 27, 2018 mass shooting in Pittsburgh, the federal prosecutor's office said.

President Joe Biden's Justice Department has put a moratorium on federal executions, however, meaning it is not clear whether the sentence will ever be carried out on Bowers.

The 50-year-old was found guilty in June of all 63 charges levelled against him, including hate crimes resulting in murder and attempted murder.

Bowers methodically tracked down his victims at Pittsburgh's Tree of Life synagogue, shooting many times from close range as he yelled "All Jews must die!"

The massacre compounded fears of a resurgence of far-right extremists and neo-Nazis across the United States.

Bowers, who had an AR-15 semiautomatic assault rifle and three Glock handguns, carried out the slayings during Shabbat – the Jewish day of rest. He had expressed strong anti-Semitic views online.

He was arrested at the scene of the attack, which left several police officers and two additional worshippers with non-fatal wounds.

Donald Trump, then the US president, called for Bowers to receive the death penalty, which federal prosecutors formally requested in August 2019.

Wednesday's verdict marks the first time federal prosecutors have sought and won a death sentence during Biden's presidency.

It has not, however, carried out any executions since he came to power in January 2021.

Attorney General Merrick Garland imposed a moratorium on executions in July 2021 after the Trump administration oversaw a record 13 executions in its final months.

For Bowers to be executed, the moratorium would need to be lifted or a new president come to power. (AFP)