Inflammatory Bowel Disease (IBD) is an incurable disease characterised by episodic and disabling inflammation of the gut.  The healthy gut microbiota regulates the tenor of host intestinal mucosal immunity and predisposition to inflammation.  With that context, the healthy and IBD gut microbiota differ – notably, the IBD microbiome is characterised by a state of “dysbiosis” with a reduction in the abundance of key Firmicutes taxa affiliated with Clostridium cluster IV and XIVa, and an expansion of pro-inflammatory pathobionts.  The gut microbiota has co-evolved with the mucosal immune system raising the intriguing possibility that it fulfils a key ecological role as an extrinsic regulator of inflammatory tone.  To explore this possibility, we used an innovative approach termed metaparental mating to selectively isolate genetically tractable Firmicutes affiliated bacteria and assessed the ability of 24 isolates to suppress NF-κB activation using our LS174T and Caco-2 gut epithelial reporter cell lines.  NF-κB is a master regulator of inflammation and is central to the pathogenesis of IBD.  From this screen we identified Enterococcus faecalis AHG0090 and strains affiliated with Clostridium cluster XIVa (AHG0001, AHG0002, AHG0011) and XV (AHG0017) that produced potent low molecular weight NF-κB suppressive bioactives (Z-score <-3).  Critically, none of the suppressive strains exhibited cytotoxic activity.  NF-κB suppression was affected by culture conditions and there were dramatic intraspecies variations in suppressive capacity.  The bioactives could be broadly separated into two classes possibly inclusive of both peptides and small molecules:  The first class are heat and proteinase K labile (e.g. AHG0011 and AHG0090) while the second class are resistant (e.g. AHG0001, AHG0002 and AHG0017).  The isolates suppressed NF-κB-p65 subunit nuclear translocation in Caco-2 cells and pro-inflammatory IL-8 secretion in peripheral blood mononuclear cells and gut epithelial organoids from healthy and IBD subjects.  Our findings show the extent of microbe-derived NF-κB suppressive capacity is more common than previously appreciated, and a loss of extrinsic NF-κB regulatory capacity from the gut ecosystem may contribute to IBD risk and recurrence.