Her Irish counterpart, Leo Varadkar, is also in Belfast, fuelling speculation that a deal on power-sharing could be imminent.
In a statement, Downing Street said Theresa May “will take part in a series of meetings with the political parties… and encourage them to reach a resolution for the benefit of the people of Northern Ireland”.
“She will make clear that the UK government remains fully committed to the restoration of powersharing devolution and the Belfast Agreement,” it added.
Mrs May is expected to tell the parties that she believes progress has been made and to reiterate that both governments will continue to work with them to see agreement reached.
“The Prime Minister will also remind the parties of the many pressing issues facing Northern Ireland and restate her strong belief that a fully functioning Executive… is the best way to serve the interest of the whole community,” the Downing Street statement said.
A spokesman for the Irish Prime Minister said: “The Taoiseach and the Prime Minister will assess the state of play in the negotiations to restore the Northern Ireland Executive and Assembly.
“The Taoiseach will use his visit to encourage the parties to reach an agreement so that functioning institutions can commence work again in the interests of the people of Northern Ireland.
“The government has consistently said that the restoration of the institutions is essential in the context of the Good Friday Agreement and that it will continue to work very closely with the British government to support the northern parties to achieve this outcome.”
It is 13 months since Northern Ireland’s devolved government collapsed, after Arlene Foster refused to stand down as First Minister over a botched renewable energy scheme.
Sinn Fein has consistently refused to resume power-sharing without a commitment to introduce both an Irish Language Act and same-sex marriage in Northern Ireland.
Last month, the new Northern Ireland Secretary, Karen Bradley MP, told the parties time was short but “one last opportunity to reach agreement” remained.
Without an agreement on devolved government soon, Northern Ireland faces the very real prospect of a return to direct rule from Westminster for the first time in a decade.