Voting on an article of impeachment for “incitement of insurrection” is under way.
During a debate in the House of Representatives, speaker Nancy Pelosi asked Republicans and Democrats to “search their souls” ahead of the historic vote. Mr Trump would be the first American president to be impeached twice.
Ms Pelosi called Mr Trump a “clear and present danger to the nation we all love”.
Actual removal seems unlikely before the January 20 inauguration of President-elect Joe Biden.
A spokesman for Senate majority leader Mitch McConnell said the Republican leader would not agree to bring the chamber back immediately, all but ensuring a Senate trial could not begin at least until January 19.