In Emily of New MoonEdit
Lofty John Sullivan was one of Father Cassidy's parishoners, and Emily Byrd Starr once came to him for help when a dispute led Lofty John to threaten the New Moon Murrays to cut down the bush that grew in between their properties and acted as a winter protection for the Murrays' garden. Father Cassidy welcomed her in the most amiable fashion, offered her plum cake and listened to her story as well as some of her poetry, encouraging her to keep on writing. Father Cassidy later had a conversation with Lofty John which dissuaded the man from cutting down the bush. Emily's aunts were upset that she'd had dealings with a Catholic priest, but were rather relieved to keep the bush intact.
After his encounter with Emily, Emily never saw him again.
Father Cassidy is described as "big and broad-shouldered with brown eyes and brown hair" with a deeply tanned face.
The character of Father Cassidy was replaced by a much younger French priest called Father Ducharme on the Emily of New Moon television series. Emily had a very different experience when meeting him, starting with a vision of several monks and a statue crying blood at White Cross. The priest told Emily about the value of the bush and that God did care about it as he even cared about the death of a little bird. Father Ducharme's interaction with Lofty John was difficult as the series' character was depicted as mentally insane and later taken to an institution. Father Ducharme intervened later on with the Murray family on different occasions.