Campylobacter jejuni and Campylobacter coli are two zoonotic pathogens with a wide host range that differ by about 15% at the nucleotide level. Campylobacter coli is largely restricted to ducks but two lineages have invaded agriculture, namely the ST828 complex and the ST1150 complex which colonize chickens and pigs. Remarkably, both lineages have undergone an enormous adaptive introgression of up to 35% of their genome from Campylobacter jejuni. We use more than 500 ST828 genomes and a large collection of isolates from C. jejuni and non-agricultural C. coli in order to describe the ongoing pattern of introgression.