Hundreds of people are expected to attend a memorial in Minneapolis for African American George Floyd, who died in police custody last month.
The death of Floyd, whose neck was pinned under a white officer's knee, has sparked huge protests over racism and police killings of black Americans.
The tribute comes despite fears over coronavirus at large gatherings.
New charges were announced on Wednesday against all four of the now sacked officers present at Floyd's death.
The charge against Derek Chauvin has been elevated to second-degree murder while the other three officers, previously uncharged, face counts of aiding and abetting murder.
The vast majority of demonstrations over the past eight days have been peaceful, but some have turned violent and curfews have been imposed in a number of cities.
Former President Barack Obama and Meghan, the Duchess of Sussex, are among senior public figures who have offered their support to the protesters.
They were joined on Wednesday by former Defence Secretary James Mattis, who also attacked his former boss President Donald Trump, saying that he stoked division and had abused his authority in his reaction to the protests.
What will happen at the memorial?
The event, in the northern city of Minneapolis where Floyd died, is the first of several to honour him.
It will take place at a sanctuary at the city's North Central University.
"It's going to be a celebration of life, but it's also going to be a plea to America and a plea for justice that we don't let his death be in vain," he told NBC's Today show.
Veteran civil rights campaigner, Rev Al Sharpton, will deliver the eulogy for the two-hour service, which will start at 13:00 local time (18:00 GMT).
"Out of all the years that I've been marching and protesting and doing eulogies and speeches, I'm more hopeful going to this service than I have been in a long time," Rev Sharpton said on MSNBC's Morning Joe programme.
"Because I see more Americans of different races and different ages standing up together, marching together, raising their voices together… That makes me know we're on the brink of real change."
More on George Floyd's death
Rev Sharpton, who met Floyd's family on Wednesday, said he would announce the launch of a new social movement at the memorial, as well as call for new federal legislation to end racial discrimination by police.
Further tributes will be held at Floyd's birthplace in North Carolina on Saturday, and in his home town of Houston on Monday.
What was Barack Obama's reaction to the protests?
Mr Obama said it was vital to channel the momentum built up in the recent protests to bring about change.
In his first video comments since Floyd's death, he said the demonstrations were as profound as anything he had seen in his lifetime, and called on Americans to seize the chance to deal with the underlying problems in society.
"Too often some of that violence has come from folks who were supposed to be serving and protecting you," Mr Obama said.
"I want you to know that you matter. I want you to know that your lives matter, your dreams matter.
"There is a change in mindset that's taking place, a greater recognition that we can do better," he added.
Mr Obama did not comment directly on Mr Trump's handling of the unrest, although he urged mayors around the country to review their use-of-force policies.
The Duchess of Sussex has also issued a personal message about Floyd's death, saying his life mattered and recent events had been devastating.
What's the background?
George Floyd, 46, was stopped by police investigating the purchase of cigarettes with counterfeit money on 25 May in Minneapolis.
A video showed Floyd being arrested and a white police officer continuing to kneel on his neck for several minutes even after he pleaded that he could not breathe.
Protests erupted and have continued since, across many US cities and also internationally, with rallies on Wednesday in Australia, France, the Netherlands and in the UK, where thousands gathered in central London.
Floyd's death follows the high-profile cases of Michael Brown in Ferguson, Missouri; Eric Garner in New York; and others that have driven the Black Lives Matter movement in recent years.
For many, the outrage over Floyd's death also reflects years of frustration over socio-economic inequality and discrimination.
Protests over the death continued in dozens of cities on Wednesday night despite widespread curfews.
They have been largely peaceful, with cities such as Los Angeles and Chicago relaxing their restrictions amid hopes that the worst of the violence had passed.
A post-mortem examination has revealed that Floyd had the coronavirus in early April. But officials stressed that this played no role in his death.
US protests timeline
George Floyd dies after being arrested by police outside a shop in Minneapolis, Minnesota. Footage shows a white officer, Derek Chauvin, kneeling on Mr Floyds neck for several minutes while he is pinned to the floor. Mr Floyd is heard repeatedly saying "I cant breathe". He is pronounced dead later in hospital.
Four officers involved in the arrest of George Floyd are fired. Protests begin as the video of the arrest is shared widely on social media. Hundreds of demonstrators take to the streets of Minneapolis and vandalise police cars and the police station with graffiti.
Protests spread to other cities including Memphis and Los Angeles. In some places, like Portland, Oregon, protesters lie in the road, chanting "I cant breathe". Demonstrators again gather around the police station in Minneapolis where the officers involved in George Floyds arrest were based and set fire to it. The building is evacuated and police retreat.
President Trump blames the violence on a lack of leadership in Minneapolis and threatens to send in the National Guard in a tweet. He follows it up in a second tweet with a warning "when the looting starts, the shooting starts". The second tweet is hidden by Twitter for "glorifying violence".
A CNN reporter, Omar Jimenez, is arrested while covering the Minneapolis protest. Mr Jimenez was reporting live when police officers handcuffed him. A few minutes later several of his colleagues are also arrested. They are all later released once they are confirmedRead More – Source