Rome's historic Trevi Fountain will be dyed red in recognition of Christian martyrs around the world.
Catholic charity Aid to the Church in Need (ACN) is organising the demonstration on April 29 to "call attention to the drama of anti-Christian persecution".
The Chaldean Catholic Bishop of Aleppo, Antoine Audo, will share testimony of the persecution Christians face in the Middle East, alongside other witnesses to Christian massacres in Yemen, Pakistan, Turkey, Kenya and Nigeria.
ACN said it hopes this will mark "the start of a long lasting, concrete reaction everywhere so that the persecuted people of the 21st century can as soon as possible return to fully enjoying their natural right to religious freedom."
It is crucial, the charity said, that "the systematic violation of the right to religious freedom, especially that of Christians... become the central issue of the public debate."
The international president of ACN, Cardinal Mauro Piacenza, will introduce the event.
The initiative is supported by a number of organisations including Communion and Liberation, Caritas Italy, the Christian Workers Movement and the Focolare Movement.
The atrocities committed against Christians, Yazidis and other minorities in the Middle East by ISIS were labelled a 'genocide' by the House of Commons on Wednesday. The European Parliament passed a similar motion unanimously in February and the US secretary of state John Kerry declared ISIS was "genocidal" in March.
2015 saw "the most violent and sustained attack on Christian faith in modern history", according to Christian persecution organisation Open Doors.
"The persecution of Christians is getting worse, in every region in which we work – and it's getting worse fast," said Lisa Pearce, Open Doors' CEO.