Most of our knowledge of Chad comes from the writings of the Venerable Bede. Bede tells us that he obtained his information about Chad and his brother, Cedd, from the monks of Lastingham, where both were abbots. Bede gives this attribution great prominence, placing it in the introduction to his work. This may indicate that the brothers had become controversial figures: certainly Bede must have thought that his material about them would be of more than usual interest to the reader. Bede also refers to information he received from Trumbert, "who tutored me in the Scriptures and who had been educated in the monastery by that master", i.e. Chad. In other words, Bede considered himself to stand in the spiritual lineage of Chad and had gathered information from at least one who knew him personally.
Chad was one of four brothers, all active in the Anglo-Saxon church. The others were Cedd, Cynibil and Caelin. Chad seems to have been Cedd's junior, arriving on the political scene about ten years after Cedd. It is reasonable to suppose that Chad and his brothers were drawn from the Northumbrian nobility. They certainly had close connections throughout the Northumbrian ruling class. However, the name Chad is actually of British Celtic, rather than Anglo-Saxon origin. It is an element found in the personal names of many Welsh princes and nobles of the period and signifies "battle". This may indicate a family of mixed cultural or ethnic background with roots in the original Celtic population of the region.
The only major fact that Bede gives about Chad's early life is that he was a student of Aidan at the Celtic monastery at Lindisfarne. In fact, Bede attributes the general pattern of Chad's ministry to the example of Aidan and his own brother, Cedd, who was also a student of St. Aidan.
Aidan was a disciple of Columba and was invited by King Oswald of Northumbria to come from Iona to establish a monastery. Aidan arrived in Northumbria in 635 and died in 651. Chad must have studied at Lindisfarne some time between these years.
Chad later travelled to Ireland as a monk, before he was ordained as a priest. Bede's references to this period are the only real evidence we have for dating the earlier part of Chad's life, including his birth.