Utilising next generation sequencing to interrogate saturated bacterial mutant libraries provides an unprecedented means to determine genome-wide gene essentiality. We developed a barcoded transposon directed insertion-site sequencing (TraDIS) system to define an essential gene list for Streptococcus equi subsp. equi, the causative agent of strangles in horses, for the first time. Six barcoded variants of pGh9:ISS1 were designed and used to generate mutant libraries that each contained between 33,000-66,000 unique mutants. Combining these data into a master library of 208,531 mutants detected an ISS1 transposition on average every 9 bp in coding sequences throughout the genome. These data identified 422 essential genes, representing 19.5 % of the S. equi genome. The gene essentiality data for this Lancefield group C Streptococcus was compared to that of group A and B streptococci, identifying concordances of 90.2 % and 89.4 %, respectively and an overall concordance of 83.7 % between the three species. Our data provides further evidence of the close genetic relationships between these important pathogenic bacteria and provides a solid foundation towards reporting the functional genome of streptococci.