Brideshead Revisited is abundant with insights into its characters' views on religion. Charles Ryder, who is agnostic, grew up with minimal exposure to religious teachings. Each Flyte family member presents a unique perspective on Catholicism. In the first chapter of the book, Charles's cousin Jasper cautions him, "Beware of the Anglo-Catholics—they're all sodomites with unpleasant accents. In fact, steer clear of all the religious groups; they do nothing but harm." Throughout the story, Charles interacts with the Flyte family about their faith, often ridiculing religion until he has a realization at the novel's end.

Sebastian is a believer who finds it challenging to follow the strictures of Catholicism. He admits in book one, chapter four, "Oh dear, it's very difficult being a Catholic." In this same chapter, he and Charles have their initial conversation about Catholicism, where Charles is surprised that Sebastian accepts the "awful lot of nonsense" associated with Catholic beliefs, such as the story of Christ's birth. Sebastian replies, "Is it nonsense? I wish it were. It sometimes sounds terribly sensible to me." His life is a continuous struggle between his personal desires and the expectations of his church. After years of battling alcoholism and wandering, Sebastian eventually assists at a monastery in Tunis, symbolically returning to his faith while remaining worldly.

Lord Marchmain is openly disdainful of Catholicism, having left the Church when he separated from Lady Marchmain. Like Sebastian, he seems to reconcile with his faith in the second book, chapter five, when, on his deathbed, he silently shows regret for his sins in response to a priest's questions. Despite his earlier cynicism towards religion and Catholicism, Charles finds himself whispering a short prayer upon witnessing this scene. Lady Marchmain is a devout Catholic and states in book one, chapter five, that the Flyte family "must make a Catholic of Charles." Her refusal to permit Lord Marchmain a divorce stems from her deep Catholic beliefs.

As a child, Cordelia attends a convent and tells Charles she will pray for him since he is an agnostic. Her youthful affection for religion is evident in acts like saying a novena (a series of prayers recited for nine days) for a pet that passed away. As an adult, her dedication to God is demonstrated through her charitable work as a nurse during wartime. She is the only Catholic character who truly seems to embrace her faith and her bond with God. Conversely, Brideshead is Catholic only by birth, showing little genuine interest or enthusiasm for the faith. His remarks on religion are mostly legalistic, such as when he discovers that Rex cannot wed Julia in the Catholic Church due to his divorce.

For much of the book, Julia appears largely indifferent to her Catholic faith, perceiving it primarily as a barrier to marrying someone of her social class. It is not until the novel's end, after she initiates her affair with Charles and divorces Rex, that she begins to seriously reflect on her Catholic beliefs. Despite her affection for Charles, she is troubled that her actions—her "waywardness and willfulness, a less disciplined habit than most of her contemporaries" during her youth, along with her forbidden relationship with Charles—have led her into sin. After her father's death, when she tells Charles she can no longer be with him, she admits, "I've always been bad. Probably I shall be bad again, punished again. But the worse I am, the more I need God." In the Epilogue, Charles is depicted saying a quiet prayer in the Brideshead chapel, feeling content that it remains open years after his last encounter with the family.