May, who begins a two-day visit to the US on Thursday during which she will become the first foreign leader to meet Trump since his inauguration, will praise the President's attempts to "renew" America.
As the UK prepares to leave the European Union, May is keen to strengthen ties with the world's top economy. But while Trump has expressed his openness to a new trade deal with the UK, he has indicated a desire to prioritize American jobs with his "America First" agenda.
May, meanwhile, has been accused of "grovelling" to Trump and chastised for meeting with a leader who has advocated torture, been accused of misogyny and has questioned global warming.
May will travel to Philadelphia Thursday to become the first serving foreign leader from outside the US to speak at the annual congressional Republican retreat. She will meet Trump at the retreat, and he will then host her at the White House on Friday.
According to remarks released by UK officials in advance, May will say that as Britain exits the EU it will have "the opportunity to reassert our belief in a confident, sovereign and global Britain, ready to build relationships with old friends and new allies alike."
"So as we rediscover our confidence together -- as you renew your nation just as we renew ours -- we have the opportunity -- indeed the responsibility -- to renew the special relationship for this new age. We have the opportunity to lead, together, again," May will say.
She is expected to tell lawmakers that the US and UK together "made the modern world."
"The institutions upon which that world relies were so often conceived or inspired by our two nations working together," she is due to say.
"It is through our actions over many years, working together to defeat evil or to open up the world, that we have been able to fulfill the promise of those who first spoke of the special nature of the relationship between us. The promise of freedom, liberty and the rights of man."
Her trip will also be an exercise of charming the first family -- she will give First Lady Melania Trump a hamper of British goods from the town of Chequers, including apple juice, damson jam, marmalade, Bakewell tarts and cranberry-and-white-chocolate shortbread.
In a nod to Trump's Sottish heritage, May will also give President Trump a quaich, a traditional Scottish cup of friendship.
May accused of 'grovelling'
But May travels to the US in the wake of a chorus of criticism, some of it from her own side.
Sarah Wollaston, an MP from May's Conservative Party, said on Twitter
that a nation "cannot lead on a global stage by advocating torture, disgusting racial stereotyping & turning back the clock on women's rights worldwide."
Vince Cable, a Liberal Democrat who was Secretary of State for Business in the previous coalition administration, , accused May of "groveling" to Trump for a trade deal, calling it an "appalling error."
In Parliament on Wednesday, MPs urged May to tackle Trump over his positions on torture, women's rights and climate change.
Ed Miliband, a former leader of the opposition Labour Party, told May she had a responsibility to the entire international community to set the tone right with Trump.
May said she was not afraid to "speak frankly" with Trump.
British Foreign Secretary Boris Johnson defended May, calling her trip to Washington "significant."
"Far from being at the back of the queue, we are now at the front of the line with the Trump administration. And I think it is very significant that tomorrow Theresa May will become the first British prime minister to be received in the White House by a new American president in his first week of office. And I'm very hopeful for the relationship that they will forge."