Graham’s accounts of the Williamite War in Ireland are of enduring importance, because he researched the subject at a time when there existed written records and oral traditions that have since been lost. As early as 1829, an Irish commentator observed that he had "rescued from oblivion important facts of our general and local history, long buried among nearly forgotten records of our country and which but for his indefatigable research must have been lost to posterity". And in 1861 it was doubted that the Siege of Derry "would ever have supplied the magnificent episode devoted to the subject in Macaulay’s "History" had the labours of the humble Rector of Tamlaghtard not gone before to facilitate the researches and kindle the enthusiasm of the noble historian".