Fr Gabriel Egan took the selfie standing in the pulpit at the Redemptorist church at Mount St Alphonsus during the Solemn Novena.
It has already been seen by more than 200,000 people.
Fr Egan said: “It was a kind of spur-of-the-moment thing. I got the notion to try a selfie at the Novena.
“It was during a warm-up period about 10 minutes beforehand, and I said ‘let’s try one together for the fun of it and see how it goes’ to the congregation in the church.
“I had my phone in my pocket. Selfies can be quite hard to take at times, but this one came out very well.”
Fr Egan said Pope Francis encourages clergy to use all forms of technology to spread the Gospel.
“And if that means using something like selfies, which for a lot of people can be fun, it gets the message out,” Fr Egan said. “As well as over 200,000 people seeing it, many have commented to me on it.”
While Facebook is seen mostly by young people, Fr Egan said many older people are using the website and are familiar with it.
“I met people at the Novena who saw it and said that it reminded them that the Novena was on,” he said. “Some of the comments on Facebook remarked that the selfie was cool and that it was nice to see the Church using something like that.”