Stephen Sim Neung-seok was born in Hoengseong, Gangwon-do. He learned the catechism from Pak Seong-go who lived in Gwangju, Gyeonggi-do in 1838. He was baptized by Father J. Chastan who was invited to his house.
Stephen moved to Sanuisil in Yongin around 1845 and then he again moved to Gyechon in Gangneung around 1862. Prior to that, he received the Sacrament of Confirmation from Bishop J. Ferréol and the Sacrament of Reconciliation from Father N. Calais, Father H. Dorie, Bishop S. Berneux.
As the Byeongin Persecution broke out in 1866, Stephen Sim Neung-seok who was living in Gyechon, Gangneung was on the run for a while, moving from place to place. He came back to Gyechon when the persecution subsided. About that time, Anthony Yi Yu-il fled to Gyechon and Stephen led a life of faith along with him. When Stephen and Anthony had a meeting with neighbors on June 24, 1868, police from the Police Headquarters raided Gyechon led by an informer. They arrested Anthony first and then Stephen, the house owner who was with Anthony.
At that moment, Stephen told the policemen, “We will not run away even though you do not tie us with cords. Please allow me to go home so that I can pay my debt to others and also put all my affairs straight. After that, please confiscate my property.” He was sent to JwaPodocheong in Seoul after putting all his affairs in order with the permission of the policemen.
While being interrogated and tortured at the Police Headquarters, Stephen did not inform on any Catholics by saying, “I have no fellow believers to report on because I was on the run from the police, moving from place to place.” When he was ordered to apostatize, he witnessed to his faith firmly by saying, “How can I apostatize? I only wish to die as quickly as possible.”
Furthermore, when Anthony who was arrested with him showed some weakness, Stephen encouraged him with all his strength to reaffirm his intention to die a martyr. After that, Stephen was taken to prison. One day, a jailer came and said to him, “You will be executed tonight, so exchange your clothes with mine.” It was said that at that moment Stephen was so glad to hear this and showed himself to be free from fear of death. He died a martyr due to severe torture after June 30. Stephen Sim was 49 years old.