Patriarch Raphael I, who is president of the assembly of Catholic Bishops in Iraq, called on "all people of good will" to "combine our voices and our hearts before the Lord in order to ask for peace."
Aid to the Church in Need is co-ordinating the plans and is aiming for Christians across the UK to take time to pray about Iraq today, the feast of the Transfiguration.
The Transfiguration is one of the twelve great feasts of the Eastern Church - which is why it has been selected as the date for combined prayer.
Aid to the Church in Need spokesman John Newton told Premier: "What we're hoping is that all the Christians in the UK and indeed around the world will join together in one big concerted effort of prayer to beseech Our Lord for peace for Iraq and peace for all those Christian's who've been driven out of their homes in the Mosul region."
A prayer has been released for the day:
"Lord,
The plight of our country
is deep and the suffering of Christians
is severe and frightening.
Therefore, we ask you Lord
to spare our lives, and to grant us patience,
and courage to continue our witness of Christian values
with trust and hope.
Lord, peace is the foundation of life;
Grant us the peace and stability that will enable us
to live with each other without fear and anxiety,
and with dignity and joy.
Glory be to you forever."
Listen to Premier's Antony Bushfield speaking to Aid to the Church in Need spokesman John Newton: