The US House of Representatives will vote on Wednesday on sending articles of impeachment against President Donald Trump to the Senate, Democrats say.
The vote sets the stage for Mr Trump’s impeachment trial to begin in earnest next week.
Mrs Pelosi has been withholding the articles of impeachment in a row with Republicans over allowing witnesses.
Mr Trump was impeached by the House last month, on accusations of abuse of power and obstruction of congress.
He denies trying to pressure Ukraine to open an investigation into his would-be Democratic White House challenger Joe Biden.
Mr Trump has been touting unsubstantiated corruption claims about Mr Biden and his son, Hunter, who accepted a lucrative board position with a Ukrainian energy firm while his father handled American-Ukraine relations as US vice-president.
The impeachment trial by the Senate will be only the third ever of a US president.
While Democrats control the House, Mr Trump’s fellow Republicans control the upper chamber 53-47, and are all but certain to acquit him.
What’s the next step?
“The American people deserve the truth, and the Constitution demands a trial,” said Mrs Pelosi, a California congresswoman, in a statement about Wednesday’s vote.
Once the resolution is approved, the House managers will walk to the Senate and formally present the articles of impeachment in the well of the chamber, escorted by the sergeant-at-arms. The articles of impeachment will be read out.
Senate leader Mitch McConnell met Republican senators behind closed doors on Tuesday to map out the ground rules.
He said the trial was likely to begin in earnest next Tuesday.
The first couple of days will involve housekeeping duties, possibly later this week.
Supreme Court Chief Justice John Roberts will be sworn in to preside, and he will administer an oath to all 100 senators to deliver “impartial justice” as jurors.
Lawmakers may hear opening arguments next week. The House managers will lay out their case against Mr Trump, and the president’s legal team will respond.
The trial is expected to last up to five weeks, with the Senate taking only Sundays off.
What does President Trump say?
Mr Trump suggested over the weekend that he might prefer simply dismissing the charges rather than giving legitimacy to the “hoax” case against him.
But Senator Roy Blunt of Missouri, who is part of the Senate leadership, said on Monday that the chamber did not have the votes to simply dismiss the charges.
Moderate Republican senators Susan Collins of Maine and Mitt Romney of Utah have made clear they would oppose any such motion.
The White House said on Tuesday the president is “not afraid of a fight” in his trial.
Deputy press secretary Hogan Gidley said Mr Trump was in fact eager for witnesses to testify that “this man did nothing wrong”.
Will there be witnesses?
One of the biggest sticking points between House Democrats and Senate Republicans has been whether testimony will be allowed during the trial.
The Senate’s trial plan will guarantee votes on whether to call witnesses and hear new evidence, Republican senators Lindsey Graham and Mike Rounds said on Tuesday.
It takes just 51 votes to approve rules or call witnesses, meaning four Republican senators would have to side with Democrats to insist on testimony.
The White House is understood to have identified several possible defectors in the Republican ranks, including Ms Collins and Mr Romney.
The others are Senators Lisa Murkowski of Alaska, Cory Gardner of Colorado and Lamar Alexander of Tennessee, who is retiring this year.
Ms Collins said: “My position is that there should be a vote on whether or not witnesses should be called.”
Mr Romney said he wants to hear from John Bolton, the former National Security Adviser, who has said he would only testify if served a legal summons.
“I expect that barring some kind of surprise,” said Mr Romney, “I’ll be voting in favour of hearing from witnesses after those opening arguments.”
Republicans say that if witnesses are allowed, they may try to subpoena Mr Biden and his son, and the unidentified government whistleblower whose complaint about Mr Trump sparked the whole impeachment inquiry.