Benedict X, born Giovanni, was elected to succeed Pope Stephen IX on 5 April 1058, but was opposed by a rival faction that elected Nicholas II. He fled Rome on 24 January 1059 and is today generally regarded as an antipope.

Pope Stephen IX was the Bishop of Rome and ruler of the Papal States from 3 August 1057 to his death on 29 March 1058. He was a member of the Ardenne-Verdun family, who ruled the Duchy of Lorraine, and started his ecclesiastical career as a canon in Liège. He was invited to Rome by Pope Leo IX, who made him chancellor in 1051 and one of three legates to Constantinople in 1054. The failure of their negotiations with Patriarch Michael I Cerularius of Constantinople and Archbishop Leo of Ohrid led to the permanent East–West Schism. He continued as chancellor to the next pope, Victor II, and was elected abbot of the Benedictine monastery of Montecassino.