"Our democracy is what is at stake, the president leaves us no choice but to act.
"The facts are uncontested. The President abused his power for his own political benefit at the expense of our national security, by withholding military aid and a crucial Oval Office meeting in exchange for an announcement for an investigation into his political rival," she said at a press conference, the BBC reported.
"Sadly, but with confidence and humility, with allegiance to our founders and a heart full of love for America, today I am asking our chairmen to proceed with articles of impeachment," said Pelosi, a day after the House Judiciary Committee began considering potential charges against Trump.
In a tweet earlier on Thursday, Trump said: "If you are going to impeach me, do it now, fast, so we can have a fair trial in the Senate, and so that our country can get back to business."
Senior Trump adviser Kellyanne Conway told reporters: "We're ready for a trial."
"That's when the defence goes on the offence," she said, adding that Republicans look forward to calling their own witnesses.
The core of the impeachment process is Trump seeking an inquiry by Ukrainian President Volodymyr Zelensky into the dealings of former Vice President Joe Biden and his son, Hunter, in Ukraine, and into alleged interference by that country in the 2016 elections.
House of Representatives Judicial Committee Chair Jerry Nadler had on Wednesday launched Round 2 of the impeachment process, accusing Trump of seeking foreign interference in US elections and being willing to compromise the nation's security.
Trump had indulged in conduct that amounted to "treason, bribery or other high crimes and misdemeanours" and never before in US history had a President engaged in all three, Nadler said.
The Judicial Committee picked up the impeachment process from the Intelligence Committee, which delivered a 300-page report on Tuesday outlining the charges against Trump, based on several weeks of secret hearings and public testimony by serving and former diplomats and officials.
The main charge listed in the report is that Trump "placed his own personal and political interests above the national interests of the United States".
The Intelligence Committee also accused him of running a "scheme subverted US foreign policy toward Ukraine and undermined our national security in favour of two politically motivated investigations that would help his presidential re-election campaign".
This is the third impeachment of a President in US history - the first was against Andrew Johnson in the 19th century and Bill Clinton in the last. Impeachment was started against Richard Nixon, but he quit before it was concluded.
( With inputs from IANS )