Sozomen was born around or before 400 in Bethelia, a small town near Gaza, from a wealthy Christian family of Palestine. During his childhood, the family experienced many years of persecution under Julian. His grandfather persisted at scriptural interpretation even in the time of persecution. At one point, they even had to flee to safety from the persecution for a period of time. Despite this, the family remained faithful, and Sozomen thus enjoyed the advantage of being trained in a Christian household.
Sozomen seems to have been brought up in the circle of Alaphrion and acknowledges a debt of gratitude to the monastic order. His early education was directed by the monks in his native place. It is impossible to ascertain what curriculum he followed in these monastic schools, but his writings give clear evidence of the thoroughness with which he was grounded in Greek studies.
As an adult he acquired training as a lawyer. He studied law in Beirut and then went to Constantinople to start his career as a lawyer. While thus engaged he conceived the project of writing a history of the Church. Sozomen wrote two works on church history. His first work covered the history of the Church, from the Ascension of Jesus Christ to the defeat of Licinius in 323, in twelve books. Sozomen's second and longer work was a continuation of the first. He planned to continue the history of Eusebius, covering the period between 323 and 439. The period actually covered in his work ends at 425. He wrote it in Constantinople, somewhere around the years 440-443. He dedicated this work to Emperor Theododosius the Younger.
The source for about three-fourths of his material was the writings of Socrates Scholasticus. The literary relationship of these writers appears everywhere. The extent of this dependence cannot be accurately determined. Sozomen used the work of Socrates as a guide to sources and order. In some matters, such as in regard to the Novatians, Sozomen is entirely dependent on Socrates.
But Sozomen did not simply copy Socrates. He went back to the principal sources used by Socrates and other sources, often including more from them than Socrates did. He used the writings of Eusebius, the first major Church historian. The Vita Constantini of Eusebius is expressly cited in the description of the vision of Constantine. Sozomen appears also to have consulted the the works of Athanasius, Rufinus, Sabinus ond Olympiodorus of Thebes as well as other authorities. He also used oral tradition, adding some of the most unique value to his work.