Her green eyes gleaming with determination, Sinéad O’Connor stares into the cameras at the Saturday Night Live studio – in the bowels of the Rockefeller Centre in Manhattan – and holds a photograph in front of her face.

Nobody blinks or says a word. Around her, the backstage bustle continues uninterrupted. The picture is of a Brazilian street child shot dead by police death squads. It’s 3 October 1992 and O’Connor is rehearsing her cover of Bob Marley’s “War” for her performance on SNL that night. The child’s photo is a calculated distraction. For her real appearance, she’ll proffer another image entirely. And the response will be very different. Thirty years on, it remains a defining moment in the Irish singer’s life and career.

“I sing ‘War’ a cappella. No one suspects a thing,” O’Connor recalled in her 2021 memoir, Rememberings. “But at the end, I don’t...