Identifying essential genes in bacterial pathogens during infection can enhance knowledge and provide novel targets for antimicrobial agents' development. Currently, only Shigella flexneri essential genes during in vitro growth have been experimentally identified. This study used transposon insertion sequencing (TIS) to identify Shigella sonnei essential genes during Caenorhabditis elegans infection. 498 genes were predicted to be essential in S. sonnei during growth on nutrient-rich media. Some genes previously predicted to be essential in Shigella were found non-essential in S. sonnei, such as acetyl metabolism genes (aceEF, lpdA) and sulphate transport genes (cysA, cyst, cysW). Finally, 217 genes were predicted as S. sonnei virulence genes during infection, including acid resistance and biofilm formation genes which was not linked to S. sonnei virulence previously.