Recent improvements in the analysis ancient biomolecules from human remains and associated dental calculus have provided new insights into the prehistoric diet and past genetic diversity of our species. Here we present a “multi-omics” study, integrating genomic and proteomic analyses of two post-Last Glacial Maximum (LGM) individuals from San Teodoro cave (Italy), to reconstruct their lifestyle and the post-LGM resettlement of Europe. Our analyses show genetic homogeneity in Sicily during the Palaeolithic, representing a hitherto unknown Italian genetic lineage within the previously identified “Villabruna cluster”. We argue that this lineage took refuge in Italy during the LGM, followed by a subsequent spread to central-western Europe. Analyses of dental calculus using genomics and proteomics showed a similar oral microbiome composition as Neandertals, but distinct from later foragers and farmers, revealing also a diet based on mammals, fish and plants. Our results demonstrate the power of using a multi-omics approach in the study of prehistoric human populations.