Hugh was born in Co. Westmeath, Ireland. He and his sisters Ann and Catherine were left in Ireland when his father, Thomas, and mother, Margaret Byrne, emigrated to Montreal, Quebec in 1831. Hugh and Catherine stayed with Patrick's parents until 1841. Their sister, Ann, stayed with Margaret Byrne's sister, Eliza, who married Thomas' brother, John O'Neill. See the book "A Worthy Daughter of the O'Neills" for further details of his reuniting with his father in Montreal.