Food and diet were class markers in nineteenth-century Ireland, which became evident as nearly one million people, primarily the poor and destitute, died as a consequence of the notorious Great Famine of 1845–52. Famine took hold after a blight (Phytophthora infestans) destroyed the virtually only means of subsistence—the potato crop—for a significant proportion of the population. This study seeks to elucidate the variability of diet in mid-nineteenth-century Ireland through microparticle and proteomic analysis of human dental calculus samples (n = 42) from victims of the Famine. The samples derive from remains of people who died between August 1847 and March 1851 while receiving poor relief as inmates in the union workhouse in the city of Kilkenny (52°39’N, -7°15’W). The results corroborate the historical accounts of food provisions before and during the Famine, with evidence of corn (maize), potato and cereal starch granules from the microparticle analysis and milk protein from the proteomic analysis. Unexpectedly, there is also evidence of egg protein—a food source generally reserved only for export and the better-off social classes—which highlights the variability of the pre-Famine experience for those who died. Through historical contextualisation, this study shows how the notoriously monotonous potato diet of the poor was opportunistically supplemented by other foodstuffs. While the Great Irish Famine was one of the worst subsistence crises in history, it was foremost a social disaster induced by the lack of access to food and not the lack of food availability.