Peter Crowley was born on 13 July 1900 in the village of Ballylanders, County Limerick, as the son of local draper and postmaster Timothy Crowley (1847 - 1921), who had fought in the Fenian Rising of 1867, and Ellen Ryan Crowley (1863 - 1951). He was the second youngest of eight siblings, all but one of whom were boys. He had a well-off childhood, with the Crowleys making much profit from their drapery, which is still an open shop in the village. Crowley attended the local national school in Ballylanders.