The late pontiff will be buried on Saturday, following his death on Easter Monday aged 88.
His body will be laid out for public view from Wednesday in St Peter’s Basilica, so mourners can pay their respects to a man dubbed the People’s Pope.
The Prime Minister will join other leaders including US President Donald Trump, who had already said on social media that he and his wife Melania plan to attend the funeral.
Details of the mass, due to take place at 10am local time in St Peter’s Square and celebrated by the dean of the College of Cardinals, were confirmed on Tuesday.
The news came as the first images of the late pontiff were published.
Francis’s body was pictured lying in a private chapel in a wooden coffin dressed in red, with rosary beads draped across his hands.
Vatican secretary of state Cardinal Pietro Parolin prays in front of the body of Pope Francis laid out in state at the Vatican (Vatican Media via AP)
His death, following a cerebral stroke that led to a coma and irreversible heart failure, prompted an outpouring of tributes across the globe.
The King, who met Francis earlier this month, said he was someone who had “profoundly touched the lives of so many”, while Sir Keir described him as having been “a pope for the poor, the downtrodden and the forgotten”.
A picture of Pope Francis on display in Westminster Cathed...
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