Born in Glencullen House, Co Dublin on 30 May 1898, to Daniel O'Connell Fitz-Simon and his wife Alice Maud Bunbury MacFarlane, Christopher Fitz-Simon spent his early life at 'Moreen', in Sandyford, Co. Dublin. He was educated at Earlsfort House, Dublin and St. Edmund's, England. He completed his military training at the Royal Military College, Sandhurst, England.

His military career began when he was commissioned in December 1917 for the Prince of Wales Leinster Regiment, Birr, Co Offaly, subsequently serving during World War 1, where he was wounded at Flanders in May 1918 and awarded the Military Cross. He returned to the Leinster depot at Birr until August 1920, and subsequently served on a peacekeeping mission to Silesia (Poland) in 1921. On the disbandment of the Leinsters in 1922, he joined the King's Own Royal Regiment in December of that year and saw subsequent service in India, Sudan, England, Egypt, and Palestine. He commanded the 2nd Battalion King's Own as temporary Lieutenant-Colonel, WW2 North Africa campaign against Italy in 1940/1941. He was promoted to Lieutenant-Colonel in 1942, and subsequently served in England, Northern Ireland and Scotland commanding the 1st battalion East Surrey Regiment. In 1942, he was hospitalised and invalided from the army in 1943.

In 1945, he was appointed land agent to the Tottenham estate at Mount Callan, Co. Clare and moved to a similar post in Annaghmakerrig, Co. Monaghan, in 1948. He retired to Glencullen House, Co. Dublin in 1953 and died in June 1984.

Col. Fitz-Simon married Gladys Killen, in October 1931; she pre-deceased him. Their sons are Dr Christopher O'Connell Fitz-Simon b.1934, now in Dublin, and Nicholas O'Connell Fitz-Simon, b.1936, now in Victoria, Australia.