 His parents were Arthur Edward Knox of Castle Rea, County Mayo, (later Trotton House, Sussex) and Jane Parsons, daughter of Laurence Parsons, 2nd Earl of Rosse.In 1859, at the age of 22, he founded "The Irish Times".Knox purchased an Ensigncy in the 63rd Foot in 1854 and was promoted Lieutenant without purchase later the same year.