Campylobacter jejuni is a commensal bacterium in the intestines of animals and birds and a major cause of foodborne gastroenteritis in humans worldwide. Here we show that exposure to pancreatic amylase leads to secretion of an α-dextran by C. jejuni and that a secreted protease, Cj0511, is required. Exposure of C. jejuni to pancreatic amylase promotes biofilm formation in vitro, increases interaction with human epithelial cell lines, increases virulence in the Galleria mellonella infection model and promotes colonisation of the chicken ileum. We also show that exposure to pancreatic amylase protects C. jejuni from stress conditions in vitro suggesting that the induced α-dextran may be important during transmission between hosts. This is the first evidence that pancreatic amylase functions as an inter-kingdom signal in an enteric micro-organism.