President Donald Trump faces a single charge — “incitement of insurrection” — over the deadly riot at the US Capitol, according to a draft of the articles.
Politicians are set to introduce the legislation on Monday, with voting in midweek.
Ms Pelosi’s leadership team also will seek a quick vote on a resolution calling on Vice President Mike Pence and Cabinet officials to invoke the 25th Amendment.
The four-page impeachment bill draws from Mr Trump’s own false statements about his election defeat to Democrat Joe Biden; his pressure on state officials in Georgia to “find” him more votes; and his White House rally ahead of the Capitol siege, in which he encouraged thousands of supporters to “fight like hell” before they stormed the building on Wednesday.
A violent and largely white mob of Trump supporters overpowered police, broke through security lines and windows and rampaged through the Capitol, forcing politicians to scatter as they were finalising Mr Biden’s victory over Mr Trump in the Electoral College.
“President Trump gravely endangered the security of the United States and its institutions of Government,” the legislation said.
The bill from Representatives David Cicilline of Rhode Island, Ted Lieu of California, Jamie Raskin of Maryland and Jerrold Nadler of New York, said Mr Trump threatened “the integrity of the democratic system, interfered with the peaceful transition of power” and “betrayed” trust.
“He will remain a threat to national security, democracy, and the Constitution if allowed to remain in office,” they wrote.
Representative Adam Schiff, a Democrat, said on Monday on CBS: “We need to move forward with alacrity.”
House Speaker Nancy Pelosi says the House will proceed with legislation to impeach Mr Trump as she pushes the vice president and the Cabinet to invoke constitutional authority to force him out, warning that Mr Trump is a threat to democracy after the deadly assault on the Capitol.
The House should act to begin impeachment proceedings.
It's the only instrument wholly within our power to remove a president who has so manifestly and repeatedly violated the Constitution.
Every effort must be made to protect the country from further harm. pic.twitter.com/ym4YpiXkDd— Adam Schiff (@RepAdamSchiff) January 8, 2021
A Republican senator, Pat Toomey of Pennsylvania, joined Republican Senator Lisa Murkowski of Alaska over the weekend in calling for Mr Trump to “resign and go away as soon as possible”.
Politicians warned of the damage the president could still do before Joe Biden is inaugurated on January 20.
Mr Trump, holed up at the White House, was increasingly isolated after a mob rioted in the Capitol in support of his false claims of election fraud.
Judges across the country, including some nominated by Mr Trump, repeatedly dismissed cases and Attorney General William Barr, a Trump ally, said there was no sign of any widespread fraud.
“We will act with urgency, because this President represents an imminent threat,” Ms Pelosi said in a letter late on Sunday to colleagues emphasising the need for quick action.
“The horror of the ongoing assault on our democracy perpetrated by this President is intensified and so is the immediate need for action.”
During an interview on 60 Minutes aired on Sunday, Ms Pelosi invoked the Watergate era when Republicans in the Senate told President Richard Nixon: “It’s over.”
“That’s what has to happen now,” she said.
Mr Pence has given no indication he would act on the 25th Amendment.
If he does not, the House would move towards impeachment.
Mr Toomey said he doubted impeachment could be done before Mr Biden is inaugurated, even though a growing number of politicians say that step is necessary to ensure Mr Trump can never hold elected office again.
“I think the president has disqualified himself from ever, certainly, serving in office again,” Mr Toomey said.
“I don’t think he is electable in any way.”
Ms Murkowski, long exasperated with the president, told the Anchorage Daily News on Friday that Mr Trump simply “needs to get out”.
A third, Senator Roy Blunt did not go that far but on Sunday he warned Trump to be “very careful” in his final days in office.
On impeachment, House Democrats would likely delay for 100 days sending articles of impeachment to the Senate for trial, to allow Mr Biden to focus on other priorities.
Senator Marco Rubio, a Republican, said that instead of coming together, Democrats want to “talk about ridiculous things like ‘Let’s impeach a president’” with just days left in office.
Still, some Republicans might be supportive.
Nebraska Senator Ben Sasse said he would take a look at any articles that the House sent over.
Illinois Representative Adam Kinzinger, a frequent Trump critic, said he would “vote the right way” if the matter were put in front of him.
The Democratic effort to stamp Mr Trump’s presidential record, for the second time, with the indelible mark of impeachment advanced rapidly after the riot.
Mr Cicilline, a leader of the House effort to draft impeachment articles accusing Mr Trump of inciting insurrection, said his group had 200-plus co-sponsors.
Potentially complicating MS Pelosi’s decision about impeachment was what it meant for Mr Biden and the beginning of his presidency.
While reiterating that he had long viewed Mr Trump as unfit for office, Mr Biden sidestepped a question about impeachment, saying what Congress did “is for them to decide”.
