Ms Truss is visiting Washington, D.C. with a delegation of MPs from the Conservative friends of Ukraine group, where she will hold talks with senior Republican leaders.
As the battle for the White House next year appears increasingly likely to be a rerun of 2020’s contest between Mr Trump and Joe Biden, Ms Truss has backed the controversial businessman.
In an article for the Wall Street Journal, she said: “For as long as most of us can recall, the US has led the free world. During the Cold War, for example, it was American power that successfully held off the communist threat from the Soviet Union. Working in tandem with British Prime Minister Margaret Thatcher, President Ronald Reagan was unflinching, calling the Soviet Union an “evil empire.”
“The world would benefit from more of that kind of American leadership today. I hope that a Republican will be returned to the White House in 2024. There must be conservative leadership in the U.S. that is once again bold enough to call out hostile regimes as evil and a threat.”
She also warned Western leaders against complacency about the defeat of communism, adding that “no such victories are permanent”.
Ms Truss’s brief premiership lasted just 49 days as she was forced to quit after then chancellor Kwasi Kwarteng’s £45 billion package of unfunded tax cuts panicked the markets and tanked the pound.
The UK’s stock and bond markets lost an estimated $500 billion in value in the weeks after she took over from Boris Johnson last September, and the Bank of England was forced to take emergency measures to stabilise the economy.
Ms Truss’s endorsement of a Republican in the 2024 election is a de facto endorsement of Mr Trump, who is almost certain to win the party’s nomination. He is leading the Republican primary contest with more than 60 per cent of the vote.
Meanwhile Mr Biden has faced calls to step aside and allow a younger Democrat to compete against Mr Trump, including from the left-leaning Washington Post.