Chronic periodontitis is an inflammatory, bacterial biofilm associated disease that results in destruction of the tooth’s supporting tissues. The oral bacteria Treponema denticola and Porphyromonas gingivalis both play significant roles in progression of this polymicrobial disease and have been linked to a variety of systemic diseases. T. denticola is a proteolytic, obligate anaerobic spirochaete that has an unusual periplasmic flagella (FlgE) driven by an inner membrane motor (MotAB) coupled to a chemotaxis system (Che). The molecular details of its virulence are poorly characterized due to limitations in its genetic manipulation. The aim of this study was to determine the role of T. denticola motility and chemotaxis in polymicrobial biofilm formation with P. gingivalis. T. denticola mutants ∆flgE, ∆cheY, ∆motA and ∆motB were generated under strictly anaerobic conditions by replacement of the open reading frames with an erythromycin resistance gene. Periplasmic flagella were imaged by cryo-electron microscopy in the ∆cheY, ∆motA and ∆motB mutants but not the ∆flgE mutant as expected. The mutants were impaired in their growth and motility compared with the wild-type. The ∆cheY, ∆motA and ∆motB mutants, but not ∆flgE, had similar coaggregation rates with P. gingivalis compared with the wild-type. T. denticola and P. gingivalis formed synergistic polymicrobial biofilms in flow cell systems resulting in a significant increase in overall biomass. Polymicrobial biofilm biomass and average thickness significantly decreased with T. denticola ∆cheY relative to wild-type and the surface area to volume ratio increased. All T. denticola motility mutants also displayed reduced abilities to form polymicrobial biofilms with P. gingivalis. Conclusions: T. denticola chemotaxis and motility enhanced polymicrobial biofilm development with P. gingivalis.