A deadline expired last week in which jihadists from the militant group the Islamic State (IS) told Christians in Mosul that they must convert to Islam, pay a tax or face death.
IS warned that if they did not heed the July 19 deadline, "there is nothing to give them but the sword.”
Since then many Christians have fled their homes.
Two French priests, the Archbishop of Lyon, Philippe Barbarin and the bishop of Evry, Michel Dubost, will travel to Iraq in show of support and spend three days with Louis-Raphael Sako, the patriarch of the Asyrian church.
Ahead of their visit, Christians in France showed solidarity with the Iraqi Christians.
On Sunday evening, about five-thousand people gathered in front of Notre Dame Cathedral, ahead of a mass for peace.
Father Antoine Vairon, a priest of Chatillon told RFI: "We have to pray for this community and we have to speak about this, and counter the silence in France."
Some posters at the demonstration read: "Them today, us tomorrow."
Demonstrators voiced their fear that Christians in France might also loose their freedom of speech in the future.
Sister Nathalie Becquart told RFI that the demonstration is not about one religion against another.
"It's a problem between fanatics and people who are moderate and want peace, and you have people who want peace in all religions," she said.
The Christians of Mosul form part of one of the oldest Christian communities in the world and dates back to the first century.
On Monday the French Foreign Minister Laurent Fabius and Interior Minister Bernard Cazeneuve issued a joint statement saying it is ready to help facilitate asylum for Christians in Iraq, adding that the government is "outraged" by their persecution.