On Thursday, she will attend a summit of European leaders in Prague, with French President Emmanuel Macron among those she is expected to meet.
After a difficult Conservative Party conference dominated by internal division and backbench opposition to some of her key policies, Ms Truss travels to the Czech Republic for the meeting of the European Political Community.
As foreign secretary, she was a sceptic of the planned summit, so her decision to attend has caused some surprise.
Downing Street says Ms Truss’s talks with Mr Macron and Dutch Prime Minister Mark Rutte will focus on migration and aim to secure progress on joint operations to disrupt people-trafficking gangs.
Ms Truss is also expected to join Czech leader Petr Fiala for a working lunch.
British Prime Minister Liz Truss — in pictures
“Europe is facing its biggest crisis since the Second World War and we have faced it together with unity and resolve,” Ms Truss is expected to tell the opening plenary session in Prague.
“We must continue to stand firm — to ensure that Ukraine wins this war, but also to deal with the strategic challenges that it has exposed.”
Liz Truss's political career — in pictures
Ms Truss will seek to stress the UK’s role in European matters — including Ukraine — despite leaving the EU, Downing Street said.
“The threat was left to fester for far too long. Now, at last, we are tackling [Russian President Vladimir] Putin’s aggression head on,” the prime minister will say.
“And we should take the same approach with other challenges before us — including long-standing regional issues like energy and migration.
“Instead of the old approach which merely dealt with the symptoms, it’s time to address the fundamental causes.”