A novel halogen-free highly crosslinked supramolecular poly(cyclotriphosphazene-co-4,4'-sulfonyl diphenol) (PZS)-functionalised melamine cyanurate (MCA) hybrid nanosheet (MCA@PZS) fire-retardant (FR) was synthesised and thoroughly characterised using SEM, FTIR, XRD, and XPS analyses. The polyamide 6 (PA6) composites comprising MCA, PZS, and the MCA@PZS hybrid were prepared via the melt-blending technique. Thermogravimetric analysis combined with FTIR and mass spectroscopy revealed that during thermal degradation, the PA6/MCA@PZS composites released less toxic gases and small organic volatile compounds than the neat PA6 and composites containing solely MCA or PZS. From rheology study it confirmed that in presence of hybrid FR MCA@PZS, significantly improved the crosslinking components formation with duration of time due to the combined effect of MCA@PZS. Moreover, compared to those of neat PA6, the PA6 composite with 5 wt.% MCA@PZS exhibited enhanced fire retardation properties, with a 29.4% and 32.1% decrease in the peak heat and total heat release rates, respectively. In addition, the PA6 composites with MCA@PZS-5% achieved a V-0 rating in the UL-94 test. Finally, based on the obtained results gaseous and condensed phase, we thoroughly evaluated the flame retardant mechanism of the planer MCA nanosheets functionalised PZS which composed with P, N, and S coexist elements to enhance the FR activity of PA6.