Meeting face-to-face for the first time, the two leaders sidestepped profound differences over a string of issues ranging from the environment to the plight of migrants and the poor.
And the US President emerged from a half-hour meeting at the Vatican gushing with enthusiasm about the 80-year-old pontiff, to the point of the former TV star appearing slightly star-struck.
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"Honor of a lifetime to meet His Holiness Pope Francis," Trump wrote on Twitter before leaving Rome for Brussels and the next leg of his first overseas trip as president.
"I leave the Vatican more determined than ever to pursue PEACE in our world."
Trump later arrived in Brussels, a city he once dubbed a "hellhole", ahead of his first summits on Thursday with wary leaders of NATO and the European Union.
Trump's declaration of intent followed a keenly-anticipated encounter between the billionaire businessman and the former Jesuit priest who has made championing the poor and the third world major themes of his papacy.
In their world view and tastes, the Argentine pontiff who eschews the use of the palaces at his disposal and the luxury hotel tycoon appear worlds apart.
But if there was any friction when they finally met, it occurred behind closed doors. In front of the cameras, both men were mostly all smiles, relaxed and even jovial.
"He is something," Trump later said of his host. "We had a fantastic meeting."
The Vatican described the discussions as "cordial" and emphasised the two men's joint opposition to abortion and shared concern for persecuted Christians in the Middle East.Francis appeared more serious at the outset but also appeared to be in jovial spirits when the two men emerged after their slightly longer than scheduled chat.
'I won't forget what you said'
The pope had presented Trump with a medallion engraved with an olive tree, the international symbol of peace.
Francis also gave Trump copies of the three major texts he has published as pope, including one on the environment which urges the industrialised world to curb carbon emissions or risk catastrophic consequences for the planet.
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Trump, who has threatened to ignore the Paris accords on emissions and described global warming as a hoax, vowed to read them. A Vatican statement on the meeting highlighted "the joint commitment in favour of life, and freedom of worship and conscience."
Trump told his host as he left, "Thank you. Thank you. I won't forget what you said."
"I give it to you so you can be an instrument of peace," he said in Spanish. "We can use peace," Trump replied.
Trump's gifts included a collection of first editions by Martin Luther King and a bronze sculpture.
Trump's administration has pleased the Church by axing rules protecting tax-funded financing of family planning clinics that offer abortions. Accompanied by his wife Melania and daughter Ivanka, Trump met Francis in the private library of the Apostolic Palace, the lavish papal residence that the current pope eschews in favour of more modest lodgings.
Afterwards, the first couple were given a private tour of the Sistine Chapel and St Peter's Basilica.
While Donald dropped in on Italy's President and met Prime Minister Paolo Gentiloni, Melania visited a children's hospital and Ivanka met women trafficked from Africa for the sex trade.
In Brussels, Trump has a light schedule on Wednesday with meetings with Belgian King Philippe and Queen Mathilde and with Prime Minister Charles Michel.
On Thursday he first meets EU President Donald Tusk and European Commission chief Jean-Claude Juncker, having previously backed Britain's shock Brexit vote and saying the EU was a doomed would-be superstate.
He will then hold his first summit with the 28 leaders of the NATO military alliance, which he dubbed "obsolete" on the campaign trail, where he is expected to press them to join the US-led coalition against Isis in the wake of the Manchester attack in Britain.
Pope Francis and Trump's past spats include the pope describing plans for a border wall with Mexico as not Christian and Trump evoking a possible Islamist attack on the Vatican which would make the pontiff glad to have him as president.
But there have also been conciliatory moves. In 2013, Trump tweeted that "the new pope is a humble man, very much like me" while Francis had promised to judge the man not the image.
Trump's Vatican visit was the third leg of his overseas trip, after stops in Saudi Arabia and Israel and the Palestinian territories.
The high-profile trip has diverted attention from Trump's domestic pressures over alleged campaign collusion with Russia. With his poll numbers at a record low for a recently-elected president, he will be hoping for a boost after rubbing shoulders with the popular pope.
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