President-elect is expected to name Florida Senator Marco Rubio as secretary of state, The New York Times reported Monday night.
It quoted three people as saying that the decision is not final, but that Trump appears to have settled on Rubio, a loyalist whom passed over as his vice presidential running mate.
Rubio has been consistently named over the last week as one of the frontrunners to head US diplomacy, along with former ambassador to Germany, Ric Grenell.
He would become a key architect of Trump's second term "America First" foreign policy, with having promised to end the wars raging in Ukraine and the Middle East and avoid any more American military entanglements overseas.
Fellow Florida Senator Rick Scott sent congratulations to Rubio in a message on X, writing: "He will restore American leadership around the world, especially in Latin America, as he represents the United States with dignity and courage!"
The nomination of Rubio, a hawkish congressman with Cuban heritage, would cap a remarkable turnaround in his relations with Trump.
In 2016, when they were competing for the Republican presidential nomination, Rubio called Trump a "con artist" and the "most vulgar person to ever aspire to the presidency."
Trump belittled him as "Little Marco" and mocked him for sweating and wearing heavy makeup during TV appearances.
Rubio first made his name in foreign policy as a vociferous opponent of Cuba and its leftist allies in Latin America, particularly Venezuela.
He has since become one of the most outspoken senators against Beijing, viewing the Asian power as a major threat to US interests.
He has sought to make it more difficult for Chinese companies to operate in the US and has led congressional efforts to punish Beijing on human rights grounds over its treatment of the Uyghur minority.
Compared with Trump, he offers a more traditional US approach to foreign policy.
After Trump spoke during his campaign about Taiwan needing to pay "protection" money to Washington, Rubio spoke out in favour of the self-governing democracy and predicted that a second Trump administration would support its defence against China.
Born to Cuban immigrants in Miami, Rubio graduated with a political science degree from the University of Florida in 1993.
He was elected to the US Senate in 2010 with his campaign buoyed by the Tea Party, a far-right contingent of Republicans that coalesced in the aftermath of Barack Obama's election as president.
Trump has promised to bring global stability through American strength, but his plans for how he intends to end the war in Ukraine remain unspecified, with European allies and Ukraine concerned about unilateral US moves.
Trump is also widely reported to be on the verge of naming former army special forces veteran and noted China hawk Michael Waltz for the crucial National Security Advisor post in the White House, according to reports Monday.
Waltz, who also represents Florida in Congress as part of the House of Representatives, wrote in his recent book that the United States faced an "existential struggle" with the Chinese Communist Party.
He expressed concern about what he termed a "1930s-era, Nazi Germany-style military build up" in China during a talk at the Ronald Reagan Presidential Foundation last month.
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