A condensed version of his Masters dissertation was published as a chapter in "The great famine" (1956) edited by R. D. Edwards and T. D. Williams. In fact as documented by Cormac O Gráda, R.D. Edwards relied on his post graduate student for much of the structuring of that work, and O'Neill was able to contribute a chapter of his choosing. Sections relating to relief works were omitted, but O'Neill published these as journal articles, one of the few professional historians to study this aspect of the Irish famine at the time. He is credited with pioneering use of archival material, with one criticism of the chapter being that he focused on the famine relief administrators and not the recipients. His work was the foundation on which further work analysing the relief effort was subsequently built. As well as contributing this chapter, O'Neill was also involved in the overall formatting of the volume, and devised the questionnaire sent out by the Irish Folklore Commission. It was from this questionnaire that Roger McHugh wrote up a chapter on the folk memories of the famine, and statistical maps were devised from the data which also appeared in the volume.