Florida Senator Marco Rubio - a harsh critic turned loyalist of Donald Trump - was nominated to serve as secretary of state in the second Trump administration, the president-elect announced Wednesday.

Rubio had been gunning for the job in TV appearances and in Trump's orbit, reports said, touting his foreign policy experience.

The Florida senator serves as vice chair of the Senate Intelligence Committee and sits on the Foreign Relations Committee.

Rubio is considered a foreign policy hawk who previously said the ongoing conflict between Russia and Ukraine needs to "be brought to a conclusion".

Rubio, 53, will essentially serve as America's top diplomat. If approved, he will be the first Latino secretary of state in US history.

The Florida senator called the appointment a "tremendous responsibility" and said he was honoured to be chosen.

"As Secretary of State, I will work every day to carry out his foreign policy agenda," Rubio said on social media. "Under the leadership of President Trump we will deliver peace through strength and always put the interests of Americans and America above all else."

He is considered a foreign policy "hawk" - meaning someone who takes hard-line positions - towards Iran as well as China.

In announcing the appointment, Trump said Rubio would be a "powerful voice for freedom" and a "strong advocate" for the US.

Rubio was once a presidential contender himself when he ran for president against Trump in 2016.

The two developed a rivalry which led the president-elect to insult the Florida senator on multiple occasions, calling him "Little Marco" occasionally.

Despite that rivalry, Rubio endorsed Trump and campaigned for him.

In the 2024 election cycle, he was among the rumoured contenders for vice-president, a job that ultimately went to fellow senator JD Vance.

Rubio was first elected to the Senate in 2010. He is the son of working-class Cuban immigrants.