In a red-carpet airport welcome, Saudi King Salman bin Abdulaziz Al Saud greeted Trump, his wife Melania and his entourage shortly after they landed in the capital, Riyadh, around 06:50 GMT on Saturday.
Trump will hold a series of meetings with the king and other Arab and Muslim leaders on Saturday and Sunday, before jetting off to Israel, the occupied Palestinian territories, the Vatican, Belgium and Italy in a nine-day tour across the Middle East and Europe.
During the two-day visit to the kingdom, Trump is expected to sign a major weapons deal, give a speech on Islam and discuss the battle against "terrorism" with more than 50 leaders.
It is the first time a US president has chosen Saudi Arabia as the first stop on a maiden trip.
Trump's visit is seen as highly symbolic, as he looks to repair Washington's ties with its closest Arab ally.
During the final years of Barack Obama's US presidency, "relations had undergone a period of difference of opinion", according to Saudi officials. These differences were largely centred around the 2015 Iran nuclear deal and the Obama administration's cautions to the kingdom about the civilian toll of the war in Yemen.
Al Jazeera's Washington editor James Bays, reporting from Riyadh, said the Saudis were very "proud and excited" that the US president chose the Gulf country as his first stop.
"They want a reset of the relationship with the US. They were not happy with Obama, and they were not happy with the US policy in Yemen and in Syria," Bays said.
Ahmed Alibrahim, a Saudi political analyst, told Al Jazeera that the Saudis see this as a "great day" for relations with the US.
"We think President Trump's cabinet does understand the Saudi challenges and does understand the challenges the GCC [Gulf Cooperation Council] faces."
He added that the kingdom would like to see more "decisive statements, actions and sanctions on the Iranian regime".
|Trump was welcomed in Riyadh on Saturday by Saudi's King Salman [Mandel Ngan/AFP]|
Before the trip, Saudi Foreign Minister Adel al-Jubeir said the visit will "bolster the strategic partnership between the two countries".
He added that "several agreements will be signed, including political agreements ... and big economic agreements".
Marwan Kabalan, an analyst at the Doha Institute's Arab Center for Research and Policy Studies, told Al Jazeera the US and Saudi Arabia will discuss a strategic plan aimed at countering "extremism" as an ideological battle.
"I think both sides have high expectations of this summit, as they are expected to discuss the most pressing issues for both of them like the conflict in Yemen, the war in Syria and the war on ISIL," Kabalan said, referring to the Islamic State of Iraq and the Levant armed group, also known as ISIS.
"Trump is expected to address the entire Islamic world while trying to establish this sort of a strategic partnership with Saudi Arabia, particularly concerning groups like ISIL."
On Saturday, Trump is expected to announce an arms deal with Saudi Arabia worth more than $100bn, in what could be the biggest such agreement in history.
Speaking on condition of anonymity, US officials familiar with the package told the Associated Press news agency that the deal would include Abrams tanks, combat ships, missile defence systems, radar and communications and cybersecurity technology.
Much of the package builds on commitments made before Trump took office, although some elements are new, including weapons designed to help Saudi Arabia in an air campaign it has led in war-torn Yemen, officials said.
The Trump administration separately informed Congress on Friday that it will sell some $500m in precision-guided munitions to Saudi Arabia. These include laser-guided Paveway II bombs and JDAM kits for converting unguided bombs into "smart bombs".
Also on the agenda in Riyadh is a summit of more than 50 Arab and Muslim leaders, including those from the six nations that form the Gulf Cooperation Council, to discuss the fight against "extremism".
Announcing the meeting, the Saudi foreign ministry said the "historic summit" should be the start to "building a partnership between the Arab and Muslim worlds and the United States at various levels".
Trump is expected to give a speech on Islam, calling for unity in the fight against "radicalism" and characterising the effort as a "battle between good and evil", the AP reported, citing a draft of his speech.
The US president will avoid tough anti-Muslim rhetoric from his presidential campaign, as well as mentions of democracy and human rights, according to the draft of the speech, which remains subject to revision, AP said.
According to Al Jazeera's Bays, the meeting will also include talks on Trump's promise to restart peace talks between the Palestinians and Israelis.
"Everyone agrees that a fresh approach could be helpful in solving this long-running conflict and President Trump certainly brings that - but Arab leaders will want to hear more than optimism, they'll want to know the US president's plan to move forward," Bays said.
After the visit in Saudi Arabia, Trump will head to Israel and the occupied Palestinian territories where he will meet his "friend" Israeli Prime Minister Benjamin Netanyahu in Jerusalem and Palestinian President Mahmoud Abbas in Bethlehem.
There are no plans for Trump to bring the two leaders together, a senior US official told the Reuters news agency, saying the administration does not believe it is the "right time just yet".
Trump will then fly to the Vatican to meet Pope Francis, who has said he will give the US president an open-minded hearing, despite differences in belief on everything from climate change to policies towards refugees.
The foreign trip comes as Trump faces growing criticism at home.
As the US president jetted off to Saudi Arabia, reports by US media emerged that a senior adviser to Trump was a "person of interest" in a probe of possible collusion with Russia during last year's election campaign and that the US president had boasted to Russian officials after firing former FBI Director James Comey earlier this month.
On Thursday, Trump also denounced the announcement of special counsel to conduct an independent investigation into the alleged Russian meddling in the election and possible collusion with Trump's team.