Originally a Protestant, Father Thwaites, S.J., had planned to enter the Anglican ministry. He joined the army in 1939 at the beginning of the second world war and was sent to France. He left Paris in June 1940, two days before the Germans entered the city. In December 1941, on a troopship in the Indian Ocean, he was received into the Catholic Church. Taken prisoner in the fall of Singapore, he spent 3 years in Japanese prison camps. After the war he became a Jesuit and was ordained a priest in 1954.

Doctrinally conservative, Father Thwaites is a supporter of the traditional Latin Mass, although he does say the new rite. He writes extensively in various conservative Catholic publications such as Christian Order.

Father Hugh S. Thwaites (originally his surname was double, "Simon Thwaites") celebrated his ninetieth birthday at St Dominic's R.C. Church, Waddon, Surrey on 21st July 2007. Fr. Thwaites celebrated a Tridentine Mass before a large gathering of friends and their families, together with several priests and brothers, followed by a social gathering. He seems as young as ever in spirit, although in his homily he described himself as "living on the edge of eternity". Not just yet we hope.