Slackia heliotrinireducens (Lanigan 1983) Wade et al. 1999 is of phylogenetic interest because of its location in a genomically yet uncharted section of the family Coriobacteriaceae, within the deep branching Actinobacteria. Strain RHS 1(T) was originally isolated from the ruminal flora of a sheep. It is a proteolytic anaerobic coccus, able to reductively cleave pyrrolizidine alkaloids. Here we describe the features of this organism, together with the complete genome sequence, and annotation. This is the first complete genome sequence of the genus Slackia, and the 3,165,038 bp long single replicon genome with its 2798 protein-coding and 60 RNA genes is part of the Genomic Encyclopedia of Bacteria and Archaea project.