Prime Minister Boris Johnson, Irish President Michael D Higgins and Taoiseach Micheál Martin are among the mourners
Numerous politicians from Northern Ireland are also paying their respects, including Sinn Féin's Michelle O'Neill and the DUP's Sir Jeffrey Donaldson
Former Ulster Unionist Party (UUP) leader Lord Trimble died last week aged 77
He played a crucial role in securing the 1998 Good Friday Agreement
The Nobel Peace Prize winner was the first person to serve as first minister of Northern Ireland
Prime Minister Boris Johnson has joined mourners, shaking hands with the DUP's Sir Jeffrey Donaldson and Taoiseach Micheál Martin among others on his entry to the church.
Prime Minister Boris Johnson seated beside Taoiseach Micheál Martin at funeral of Lord Trimble
Image source, PA MediaSir Jeffrey Donaldson arrives ahead of the service at 12:30
Sinn Féin's Michelle O'Neill and SDLP leader Colum Eastwood also take their seats in the church.
Former Taoiseach Bertie Ahern has also arrived at Harmony Hill Presbyterian Church in Lisburn, as well as former Alliance leader David Ford.
Image source, ReutersFormer Taoiseach Bertie Ahern arrives at funeral of Lord Trimble
Mourners have started arriving at the church in Lisburn.
Current UUP leader Doug Beattie was one of the first to arrive, with Sinn Féin’s Gerry Adams, Michelle O’Neill, Alex Maskey and Bairbre de Brún arriving soon after.
Retired staff from UUP headquarters have also taken their places in the church.
Image source, PA MediaSpeaker of the Northern Ireland Assembly Alex Maskey, former Sinn Féin President Gerry Adams and Bairbre de Brún
Image source, PA MediaFormer Northern Ireland Secretary Owen Paterson (left) and UUP leader Doug Beattie
Welcome to our live page for the funeral of former First Minister Lord Trimble.
We'll be covering the service as it happens on the BBC News NI website and you can listen to a special extended edition of Talkback on BBC Radio Ulster from 12:00BST.
Thanksgiving service for Lord Trimble