In the 1940s, new interpretations of John's reign began to emerge, based on research into the record evidence of his reign, such as pipe rolls, charters, court documents and similar primary records. Notably, an essay by Vivian Galbraith in 1945 proposed a "new approach" to understanding the ruler. The use of recorded evidence was combined with an increased scepticism about two of the most colourful chroniclers of John's reign, Roger of Wendover and Matthew Paris. In many cases the detail provided by these chroniclers, both writing after John's death, was challenged by modern historians. Interpretations of Magna Carta and the role of the rebel barons in 1215 have been significantly revised: although the charter's symbolic, constitutional value for later generations is unquestionable, in the context of John's reign most historians now consider it a failed peace agreement between "partisan" factions. There has been increasing debate about the nature of John's Irish policies. Specialists in Irish medieval history, such as Sean Duffy, have challenged the conventional narrative established by Lewis Warren, suggesting that Ireland was less stable by 1216 than was previously supposed.

When did new interpretations of John's reign begin to emerge?