O’Cinneide was born in Toronto, Ontario and attended high schools both in Canada and the United States.

After working as an IT analyst for decades, in 2015 O’Cinneide walked the Camino de Santiago, a 500-mile pilgrimage in northern Spain.

O’Cinneide's debut novel, Petra's Ghost was promoted as literary fiction despite appearing on multiple horror genre book lists,[5][6][7][8] possibly due to a haunting that takes place as part of the story.

The novel was named one of the “summer's best horror books” by the Toronto Star where it was noted for "Structuring a novel around a traditional Christian pilgrimage" despite "the overwhelmingly secular, even atheist tone of our times.

[10] The second book in the series, Starr Sign, was nominated in 2022 by the Mystery Writers of America for a prestigious Edgar Award in the category of Best Paperback Original.