The role of Freddie Joyce is played by Brendan Gleeson's real-life son Domhnall Gleeson. The two actors share only one scene together.

Brendan Gleeson and John Michael McDonagh came up with the character of Father James at the end of their collaboration on The Guard (2011). It was tailored specifically for Brendan Gleeson, who in turn helped to develop elements of the character.

In an early scene, Father James (Gleeson) is reading a newspaper with the headline "Two hitmen hunted over Dublin murders". This is most likely a reference to McDonagh's brother's film, In Bruges, and Gleeson's role therein.

The films features 12 supporting characters. There were 12 disciples.

When it came to shooting, John Michael McDonagh almost by accident noticed how the mountain in the background gave 'this looming presence, this sinister aspect' and made a decision to include it in every shot thereafter.