Mike Haines has continued to promote inter-religious tolerance and unity against extremism since IS has released a video showing the beheading of his brother David in September 2014.
According to the Catholic Herald, the British Ambassador to the Holy See, Nigel Baker, said this was a message Mike Haines shared with Pope Francis.
Speaking ahead of the general audience, on the Feast of the Annunciation, Mr Baker said: "Mike Haines will be bringing to the Vatican his message of inter-religious understanding.
"Pope Francis has called for a common commitment to end fighting, hatred and violence. Mike Haines is living that commitment in an extraordinary way."
In October 2014, Mike Haines signed a joint letter with Barbara Henning, the widow of Alan Henning who was also murdered by Islamic State in 2014, calling for "unity of people of all faiths in our society" and urging "churches, mosques, synagogues to open their doors and welcome people of all faiths".
