A message from the Pope will be read as the requiem mass is held in London on Tuesday following a private funeral held in Southend a day earlier.
The Prime Minister and the Labour leader are both set to pay their respects to the father-of-five after he was stabbed to death while holding a constituency surgery at Belfairs Methodist Church in Leigh-on-Sea on October 15.
The Archbishop of Westminster, Cardinal Vincent Nichols, will preside and Archbishop Claudio Gugerotti, the Apostolic Nuncio to Great Britain, will deliver a message from Pope Francis.
Crowds turned out to bid farewell to Sir David for his funeral on Monday.Hundreds lined the streets of Southend as a horse-drawn carriage carried his coffin, draped in the Union flag.
Uniformed police officers bowed their heads as the hearse arrived and people applauded.Close friend and former Conservative MP, Ann Widdecombe, read a statement on behalf of the Amess family at the funeral, urging people to come together.
In it, they said their "hearts are shattered", but urged people to "please let some good come from this tragedy".
Ali Harbi Ali, 25, has been charged with his murder and also with preparing acts of terrorism between May 1 2019 and September 28 this year.
He is due to enter pleas in December.