Superantigens are a family of highly mitogenic exotoxins that are produced by only a small number of bacterial species, including Group A Streptococcus (GAS, Streptococcus pyogenes). These toxins share the ability to trigger excessive and aberrant activation of T cells which can lead to severe pathologies following infection. It has now become clear that superantigens are also important in the very early stages of nasopharyngeal colonization when the bacteria are establishing a niche. Yet, despite their critical role in the pathogenesis of infection, the molecular regulation of these toxins in incompletely understood. Here we provide new mechanistic insight into the regulatory networks controlling expression and activity of prophage-encoded superantigens (SpeA, SpeC and SSA) associated with the recent global surge in GAS infections. By establishing an inter-relationship between cytolysin-mediated cytotoxicity towards epithelial cells and superantigen SSA potency, we have provided the first description of a thiol-activated bacterial superantigen. In addition, we demonstrate that increased expression of the SpeA superantigen in the highly toxigenic GAS M1UK lineage is subject to regulation by a novel RNA–RNA base pairing interaction. To further investigate the dynamics of streptococcal superantigen production in response to environmental stimuli and stress factors, we generated luminescent reporter strains of GAS. This nanoluciferase‐based reporter tool enables real-time detection of superantigen gene expression both in vitro and in vivo and has the potential to decipher novel regulatory circuits controlling superantigen expression, providing a platform for future therapeutic target identification.