A novel halogen-free highly cross-linked supramolecular poly(cyclotriphosphazene-co-4,4'-sulfonyl diphenol) (PZS)-functionalized melamine cyanurate (MCA) (MCA@PZS) hybrid nanosheet fire-retardant (FR) was synthesized and thoroughly characterized using scanning electron microscopy, Fourier-transform infrared (FTIR), X-ray diffraction, and X-ray photoelectron spectroscopy analyses. The polyamide 6 (PA6) composites comprising MCA, PZS, and the MCA@PZS hybrids were prepared via the melt-blending technique. The 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 MCA or PZS solely. Moreover, compared to neat PA6, the PA6 composite with a 5 wt % MCA@PZS hybrid exhibited enhanced fire retardation properties, with a 29.4 and 32.1% decrease in the peak heat and total heat release rates, respectively. Besides, the PA6 composites with MCA@PZS-5% content achieved a V-0 rating in the UL-94 test. Finally, based on the obtained results from gaseous and condensed phases, the possible mechanism responsible for improved FR properties of the PA6/MCA@PZS composites was proposed.