The Taoiseach will meet the new British Prime Minister in London this weekend ahead of the state funeral for Queen Elizabeth.
Micheál Martin will meet Liz Truss at Downing Street on Sunday, where it is expected the Northern Ireland Protocol will be discussed.
He met Ms Truss in Northern Ireland earlier this week, when they attended a Service of Reflection for the queen at St Anne's Cathedral in Belfast during the visit of King Charles.
Also on Sunday, Ms Truss will meet US President Joe Biden, Canadian Prime Minister Justin Trudeau and Polish President Andrzej Duda.
Ms Truss has met Mr Biden as foreign secretary but this will be their first meeting since she became prime minister.
It will take place against a backdrop of disputes over the Northern Ireland Protocol and difficulties working towards a trade deal with the White House.
The head-to-head with Mr Biden, who will attend the funeral with First Lady Jill Biden, would ease the pressure on Ms Truss's visit to the UN General Assembly next week although No 10 did not rule out another bilateral there.
Ms Truss and European Commission President Ursula von der Leyen are also understood to be arranging a meeting while both attend the UN summit, where they are expected to discuss the dispute between the UK and the EU over the Northern Ireland Protocol.
On Saturday, Ms Truss will meet privately with her counterparts from Australia and New Zealand, Anthony Albanese and Jacinda Ardern, at the government's Chevening country residence, a No 10 spokesperson said.
Around 500 dignitaries from around the world, including President Michael D Higgins, will head to London for the state funeral, in what is set to be one of the biggest logistical and diplomatic events in the UK in decades.
They will join members of the royal family, UK prime ministers past and present and key figures from public life at Westminster Abbey - which can hold about 2,000 people - at 11am on Monday.
Germany's President Frank-Walter Steinmeier, Italy's President Sergio Mattarella and Brazil's President Jair Bolsonaro are among those attending.
But Downing Street declined to confirm reports that Ukraine's First Lady Olena Zelenska, President Volodymyr Zelensky's wife, will travel to the funeral.
King Felipe of Spain and his wife Queen Letizia are among the European royals who will attend.
Emperor Naruhito of Japan is also set to travel to London for what will be his first overseas trip since ascending the throne in 2019.
Invitations to the queen's funeral have not been sent to Russia or Belarus against the backdrop of the invasion of Ukraine.
Taliban-ruled Afghanistan has also been excluded, as has Syria and Myanmar.
The seating plan, which could prove to be highly complicated due to the various protocol and political issues thrown up by a gathering of this size, is yet to be finalised.
