O'Hara, a school teacher in the Victorian Education Department, and his wife, Mary Ann née Connelly, were both from Ireland. He was the son of John O'Hara and Mary, nee O'Neill. O'Hara's son, J. B. O'Hara (q.v.), was to have a distinguished career in teaching and literature. O'Hara's two insolvencies led to the loss of the family home.
The birth certificate of O'Hara's son has the name of the father as Patrick Kelly O'Hara as does his own death certificate. E. Morris Miller's Australian Literature from Its Beginnings to 1935 (1940): 254 says Patrick Knight O'Hara.