The event is the first of its kind at Westminster Abbey and has been organised by charities including SOS Bosnia, MAG (Mine Action Group), WarChild, CARE International and Save the Children UK.
Event details
5pm: Evensong
6pm: Wreath-laying ceremony
At the memorial for innocent victims at the West Gate
The service falls on World Humanitarian Day and will be attended by representatives of the British government, the UN and aid agencies.
It will consist of a wreath laying at the Innocent Victims Memorial and is open to the public.
Estimates suggest there are now around a quarter of a million humanitarian workers around the world as conflicts and violence increases.
Dr Elaine Laycock is a Christian and was an aid worker in Bosnia.
She told Premier she had the idea for tonight's service several years ago when her colleagues were killed.
"They came back in black plastic body bags in a cargo plane.
"No flags, no music, no ceremonies, no marching bands, nothing.
"We felt guilty, we felt shocked and we felt that there was nothing to help the relatives at that stage," she said.
The service starts at 6pm and is open to anyone.
Hear more from Dr Laycock here: