The Prince of Wales and the Duchess of Cornwall will attend the ceremony along with nearly 300 people who have lost relatives, friends and loved ones, as well as senior Government ministers.
Among the families expected will be survivors of the deadly Tunisian beach attack at Sousse in 2015, in which 30 Britons were killed.
The memorial, entitled Still Water, which was designed by Alison Wilding and Adam Kershaw.
Also present for the service at the National Memorial Arboretum in Staffordshire will be Foreign Secretary Boris Johnson, Home Secretary Sajid Javid and Tobias Ellwood, Minister for Defence People and Veterans.
Mr Ellwood, whose brother was killed in the 2002 Bali bombing, was tasked in 2015 with delivering the memorial.
Its design, as an elliptical-shaped pool surrounded by woodland, was selected by an independent panel, in consultation with victims' relatives, in 2017.
The memorial has no dominating symbolism but was chosen as it reflected the global reach of terrorism and the continuation of life.
Speaking ahead of the unveiling, Mr Ellwood said: "Today is a day when we remember the lives of those who were tragically taken in terrorist attacks abroad.
"I know from personal experience that in times of pain we must come together to support and help one another.
"This memorial stands as a symbol of our unity against violence and hatred and will be a peaceful space for families to remember their loved ones."
It is hoped that the memorial, which features seating, will become a place of reflection, remembrance and contemplation for people living with the impact of terrorism.
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