Mr Trump was acquitted largely along party lines on two articles of impeachment approved by the Democratic-led House of Representatives on 18 December, with the votes falling far short of the two-thirds majority required in the 100-seat Senate to remove him under the US Constitution.
The Senate voted 52-48 to acquit him of abuse of power stemming from his request that Ukraine investigates political rival Joe Biden, a contender for the Democratic nomination to face Mr Trump in the 3 November election.
Republican Senator Mitt Romney joined the Democrats in voting to convict.
No Democrat voted to acquit.
The Senate then voted 53-47 to acquit him of obstruction of Congress by blocking witnesses and documents sought by the House.
A conviction on either count would have elevated Vice President Mike Pence, another Republican, into the presidency.
Mr Romney joined the rest of the Republican senators in voting to acquit on the obstruction charge.
No Democrat voted to acquit.
On each of the two charges, the senators voted one by one on the Senate floor with US Chief Justice John Roberts presiding.
Senate Majority Leader Mitch McConnell and other Republicans engineered a stripped-down trial with no witnesses or new evidence.
Democrats called the trial a sham and a cover-up.
Mr Trump called the impeachment an attempted coup and a Democratic attempt to annul his 2016 election victory.
Throughout the impeachment drama, Mr Trump and his Republican allies kept up their attacks on Mr Biden's integrity.
It remains to be seen how much political damage that inflicted.
In the first of the state-by-state contests to determine the Democratic challenger to Mr Trump, Mr Biden placed a disappointing fourth in Iowa, according to incomplete results from Monday's voting.
Mr Biden has accused Mr Trump of "lies, smears, distortions and name-calling."
Mr Trump faces no serious challengers for his party's presidential nomination.
He is poised to claim the nomination at the party's convention in August and previewed in his State of the Union address on Tuesday campaign themes such as American renewal, economic vitality and hardline immigration policies.
Mr Romney, the 2012 Republican presidential nominee, broke with his party to vote to convict Mr Trump on the abuse-of-power charge.
Mr Romney called the president's actions in pressuring Ukraine to investigate Mr Biden "grievously wrong" and said Mr Trump was "guilty of an appalling abuse of public trust."
"What he did was not 'perfect,'" Mr Romney said on the Senate floor, as Mr Trump has described his call with Ukraine's president that was at the heart of the scandal.
"No, it was a flagrant assault on our electoral rights, our national security and our fundamental values. Corrupting an election to keep one's self in office is perhaps the most abusive and destructive violation of one's oath of office that I can imagine."
Mr Romney, a moderate and elder statesman in his party, paused during his speech as he became choked with emotion after mentioning the importance of his religious faith.
Republican Senator Lindsey Graham lashed out at Democrats, saying: "What you have done is unleash the partisan forces of hell."
Chuck Schumer, the top Senate Democrat, said Mr Trump's acquittal in an unfair trial was worth nothing.
"No doubt, the president will boast he received total exoneration. But we know better. We know this wasn't a trial by any stretch of the definition."
In his speech, Mr McConnell said: "The architects of this impeachment claimed they were defending norms and traditions. In reality, it was an assault on both."
Biggest victory yet
Democrats expressed concern that an acquittal would further embolden a president who already challenges political norms.
They have painted him as a threat to US democracy and a demagogue who has acted lawlessly and exhibited a contempt for the powers of Congress and other institutions.
They also have voiced concern over Russia interfering in another American election.
Mr Trump's legal team offered a vision of nearly unlimited presidential powers, a view Democrats said placed any president above the law.
The acquittal handed Mr Trump his biggest victory yet over his Democratic adversaries in Congress.
Democrats vowed to press ahead with investigations - they are fighting in court for access to his financial records - and voiced hope that the facts unearthed during the impeachment process about his conduct would help persuade voters to make him a one-term president.
Mr Trump's job approval ratings have remained fairly consistent throughout his presidency and the impeachment process as his core conservative supporters - especially white men, rural Americans, evangelical Christians and conservative Catholics - stick with him.
The latest Reuters/Ipsos poll, conducted on Monday and Tuesday, showed 42 per cent of American adults approved of his performance, while 54 per cent disapproved.
That is nearly the same as when the House launched its impeachment inquiry in September when his approval stood at 43 per cent and disapproval at 53 per cent.
The trial formally began on 16 January.
The Senate voted 51-49 last Friday to defeat the Democrats' bid to call witnesses such as Mr Trump's former national security adviser John Bolton, with only two Republicans joining them.
In the previous presidential impeachment trials, Andrew Johnson was acquitted in 1868 in the aftermath of the American Civil War and Bill Clinton was acquitted in 1999 of charges stemming from a sex scandal.
In the hours before the vote, numerous senators gave speeches on the Senate floor explaining their vote.
Shadow of investigation
Mr Trump, now seeking a second four-year term, has been under the shadow of some sort of investigation for most of his presidency.
The acquittal marked the second time in 10 months that he withstood an existential threat to his presidency.
In March 2019, Special Counsel Robert Mueller found insufficient evidence that Mr Trump engaged in a criminal conspiracy with Russia in its interference on his behalf in the 2016 election.
Mr Mueller did not exonerate Mr Trump of obstruction of justice in seeking to impede the investigation but stopped short of concluding the president acted unlawfully.
Mr Trump declared full vindication.
On 25 July, Mr Trump asked Ukrainian President Volodymyr Zelensky during a phone call to "do us a favour" and open an investigation into Mr Biden and his son Hunter Biden and into a discredited theory beneficial to Russia that Ukraine colluded with Democrats to meddle in the 2016 election to harm Mr Trump.
Hunter Biden had joined the board of Ukrainian energy company Burisma while his father was US vice president.
Mr Trump accused the Bidens of corruption without offering substantiation.
The Bidens denied wrongdoing.
Democrats said Mr Trump further abused his power by withholding $391 million in security aid approved by Congress to help Ukraine battle Russia-backed separatists and by dangling a coveted White House meeting as leverage to pressure Mr Zelensky to announce the investigations.