Through the work of the Cowley Fathers' mission, and particularly the German missionary Baroness Paula Dorothea von Blomberg he became a Christian and was one of the first to be baptized in St Philip's Mission, Sir Lowry Road, on 7 March 1886. Shortly after his baptism, Bernard started work at St Columba's Hostel, which was run by the missionaries for African men. Within a few months he was sent to Zonnebloem College to train as a catechist.
In January 1891, Bernard accompanied the new missionary bishop of Mashonaland, George Wyndham Knight-Bruce, as a lay catechist among the Shona people in Southern Rhodesia (Zimbabwe). He was sent to work in the Marandellas (Marondera) district among the Nhowe people, and settled in the kraal of Mangwende Mungati. Bernard built his home there, and took people who wanted to learn into his home to teach them the gospel. In March 1896, Bernard married Mutwa (later ‘Lily’), a granddaughter of the Mangwende and a Christian convert.
During the Matabeleland Rebellion, Bernard Mizeki was murdered outside of his home. While missionary workers were being ordered to safety, Bernard felt that his absent bishop’s orders to stay could not be overruled. On the night of 18 June 1896, he was dragged from his home and stabbed. Mutwa found him still alive and went for help. Before she could return, she and others reported seeing a great white light all over that place, and a loud noise “like many wings of great birds”. Bernard's body was then found to have disappeared. Mchemwa, a son of the Mangwende and an ally of the witch doctors, was later found to be responsible for Bernard's murder and the removal of his body, as well as the destruction of the mission settlement there.
Bernard Mizeki’s work among the Shona bore fruit. After long years of earlier mission work in Mashonaland by white missionaries, the first Shona convert to be baptised was one of the young men whom Bernard had taught: John Kapuya. John was baptised only a month after Bernard’s death, on 18 July 1896.
St Bernard Mizeki is revered as a hero of the faith in Africa. Today, Bernard Mizeki College stands close to where he lived, and the Mangwende's kraal, above the village, is crowned with a large cross to commemorate Bernard.
- Jean Cecil Farrant (1966). Mashonaland Martyr: Bernard Mizeki and the Pioneer Church. Oxford University Press. Retrieved 1 October 2013.