 His younger brother Dennis Flynn (birth name was Denis Christopher O'Flynn) was also active in Canadian politics serving as the Mayor of Etobicoke, Ontario and Chair of Metropolitan Toronto.Flynn was born Patrick Joseph "Joe" O'Flynn in Rathcormac, County Cork, Ireland on September 8, 1921.He and Denis, along with their parents, John Joseph O'Flynn and Molly O'Flynn (née Mary Cahill) immigrated to Canada in 1925 on board the CP Ship Melita.