President Michael D Higgins will meet Britain's King Charles III ahead of his coronation in London.
President Higgins and his wife Sabina will attend a reception at Buckingham Palace on Friday night.
The event will be hosted by King Charles and Queen Camilla.
Both President Higgins and Taoiseach Leo Varadkar have been invited to the coronation on Saturday.
The UK Ambassador to Ireland, Paul Johnston, has said this is "emblematic of our uniquely close relationship."
Others attending include First Minister (Designate) of Northern Ireland, Michelle O'Neill.
The Sinn Féin deputy leader has said she recognises "there are many people on our island for whom the coronation is a hugely important occasion."
Her attendance has been criticised by Aontú leader Peadar Tóibín.
"What Sinn Féin is doing here is not a million miles away from taking the oath of allegiance [and] taking seats in Westminster," he told Newstalk last week.
"Officially Sinn Féin will be attending a coronation of the King of Great Britain and the North of Ireland.
"In attending it confirms it and accepts it; unless Michelle's going to be crossing her toes and her fingers during the event.
"The corollary to what Michelle is doing is asking unionists to attend the 1916 commemoration.
"They don't have to do that to be our friends and be able to work with us on building a united Ireland".
A decision by RTÉ to dedicate four hours of programming to the event on Saturday has also been criticised by People Before Profit TD Paul Murphy.
"The British monarchy is not some benign tourist attraction," he said on Thursday.
"It is built on racism, on slavery, on empire.
"People are going to be asked on Saturday, through their TV screens, to swear allegiance to Charles.
"A man who nobody has cast a single vote for, a man who was titular head of the parachute regiment responsible for Bloody Sunday, a man who received suitcases full of cash from the Qatari prime minister.
"The idea that RTÉ - a public service broadcaster in a republic, which was colonised by the British empire - should be showing this as some major item, as opposed to featuring it for a couple of minutes in a news piece, seems to me to be quite inappropriate," he added.