Donald Trump faces a trial in the Senate after the House of Representatives voted in favour of triggering the next stage of impeachment.
The House voted largely on party lines, with 228 Democrats voting in favour, and one Democrat joining 192 Republicans to vote against sending the charges on.
Although Mr Trump is expected to be acquitted of the charges of abuse of power and obstruction of Congress, because the Republicans control the Senate, he will still be required to face a trial.
The US president is accused of abusing his office by asking the Ukrainian president to investigate the son of his political rival Joe Biden.
Addressing the House before the impeachment vote, Speaker Nancy Pelosi said: "The president violated his oath of office, undermined our national security, jeopardised the integrity of our elections."
Mr Trump dismissed the charges as a "hoax".
As Mrs Pelosi named the prosecutors, she said she had hoped to send the articles over to the Senate earlier but new evidence against the president had been revealed.
She said Democrats had found that Mr Trump spoke to Ukrainian president Volodymyr Zelensky just 21 seconds after freezing Ukraine's aid.
She added: "This is about the US constitution and it's important that Trump and Putin know that the US people choose the president, not Putin."
She said they have taken so long to impeach the president because they needed to gather evidence, which they say they have now.
The White House released a statement shortly after the House started its work.
It read: "The only thing Speaker Pelosi has achieved with this sham, illegitimate impeachment process, is to prove she is focused on politics instead of the American people.
"The Speaker lied when she claimed this was urgent and vital to national security because when the articles passed, she held them for an entire month in an egregious effort to garner political support. She failed and the naming of these managers does not change a single thing.
"President Trump has done nothing wrong. He looks forward to having the due process rights in the Senate that Speaker Pelosi and House Democrats denied to him, and expects to be fully exonerated.
"In the meantime, after President Trump signs the historic China Trade Deal greatly benefiting the people of this country, he will continue working and winning for all Americans, while the Democrats will continue only working against the president."
Before the vote, Mrs Pelosi named the House prosecutors, known as impeachment managers, who will take the case to senators.
The seven she announced are Adam Schiff, Jerry Nadler, Zoe Lofgren, Hakeem Jeffries, Val Demings, Jason Crow and Sylvia Garcia.
Lead manager and intelligence committee chairman Mr Schiff was previously a federal prosecutor in California and prosecuted the first FBI agent to be charged with espionage.
He and Mr Nadler, the judiciary chairman, will lead the team.
Ms Demings was the first female chief of police in Orlando, while Ms Garcia was the first Hispanic and first woman to be elected in her own right to the Harris County Commissioner's Court.
Ms Pelosi said she had chosen these seven carefully, and that they would launch a defence of the US Constitution.
She said: "Today, I have the privilege of naming the managers of the impeachment trial of the president.
"It is their responsibility to present the very strong case for the president's impeachment and removal. The impeachment managers represent the patriotism, pluralism and vibrancy of America.
"The House has demonstrated its courage and patriotism.
"Our managers reflect those values, and will now honour their responsibility to defend democracy for the people with great seriousness, solemnity and moral strength."
As the articles of impeachment are sent to the Senate, the whole prosecution team will line up behind House Sergeant-at-Arms Paul Irving and House Clerk Cheryl Johnson, who will hold the articles.
They will walk two-by-two to the doors of the Senate, and hand the articles to Secretary of the Senate Julie E. Adams.
Senate Republicans have indicated they will not vote to dismiss the articles without hearing the arguments, something the president suggested doing.
There is an ongoing debate over how and when witnesses will be called.
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Republicans control the Senate, the US's second chamber, by 53-47 and it would take 51 votes to approve rules or call witnesses during the trial.
If four Republican senators joined with Democrats, they could insist on new evidence.
Mr Trump's trial will be only the third in US presidential history and the second to be televised.