Trump will be tried in the Republican-controlled Senate on charges that he obstructed Congress and abused his powers.
Although the Democrat-controlled House had voted to impeach Trump On December 18, Pelosi had withheld sending the impeachment documents, which are a charge sheet framed by the House, to Senate.
This will be only the third time in the US' 243-year history that a President would be tried after impeachment and Trump can expect to be acquitted like his two predecessors, Bill Clinton in 1998 and Andrew Johnson in 1868, because there won't be a two-thirds majority to convict and remove him from office.
While there is no chance for removal of Trump from office, Democrats are hoping to use the Senate trial as a propaganda tool ahead of the elections in November by giving the charges against Trump another public airing and turning voter opinion against Republican senators facing re-election.
The trial in the Senate will be presided over Chief Justice John Roberts and the Senators are to act as jurors.
During Wednesday's vote, the House will also select impeachment managers, who will act as prosecutors at the trial.
Pelosi and the Democrats' Senate Leader Chuck Schumer had delayed sending the impeachment documents to negotiate the trial procedures to include new evidence and witnesses.
She also hoped to make some Republican senators break ranks with the leaders on the procedures for the trial and has partially succeeded in this as at least four of them appear open to witnesses being called.
Republican Leader of the Senate Mitch McConnell appeared confident that he would have a hold on his party senators to set the rules for the trial.
While Trump's conviction and ouster from office is virtually impossible because of the two-thirds vote requirement in the 100-member Senate, only a simple majority is required on procedural matters. The Republicans have 53 members and four of them shifting positions could make a difference here.
On Sunday, Trump called for an outright dismissal of the impeachment by the Senate, but many Republican Senators are against it.
Earlier, Trump had asked for a full-fledged trial that would call Democratic Party leaders and the secret whistle-blower, who set off the impeachment, to testify.
Democrats want Trump administration officials to be called to testify.
Whether witnesses would be called to testify is still open as the Republicans have said that it would be decided when the trial starts.
The charges against Trump stem from a July phone call he had with Ukraine's President Volodymyr Zelensky in which he asked him as a "favour" to investigate former Vice President Joe Biden and his son Hunter.
Democrats say that this was an abuse of power and amounted to inviting foreign interference in US elections as Biden is the leading candidate for the Democratic nomination to run against Trump in this year's election.
They also say that he withheld crucial military aid to Ukraine, a US ally against Russia, to pressure Zelensky and this endangered US national security. Trump said he delayed the aid to make sure the new government stomped out corruption.
Hunter Biden, who was made to leave the Navy because of alleged drug use and had no experience in the energy industry or in Ukrainian businesses was appointed a director of a gas company there and received monthly payments of $83,000, according to Republicans.
The former vice president, who was looking after Ukrainian affairs, had a prosecutor looking into gas company removed.
He and the Democrats say that it was because the prosecutor was corrupt, while Republicans see it as a conflict of interest.
(Arul Louis can be contacted at arul.l@.in and followed on Twitter @arulouis)
( With inputs from IANS )