The flame retardancy of thermoplastics used in the automotive sector has been a topical challenge for a long time. Halogenated flame-retarded systems have been the additive of choice for several decades. The main issues include the recycling of polymers containing such halogens and the burning of such plastics releasing toxic fumes. Due to recent regulations, their use is now prohibited and halogen-free solutions are well researched. This study aims to investigate the influence of the combination of phosphonium-based ionic liquid (IL-P) and phosphine oxide (PO) as non-halogenated flame retardants on the mechanical and flame retardancy properties of polyamide 6. Different compounds were prepared in the melt state to ensure a good homogeneity between different constituents. The pelletized strands were transformed into sheets using a cast extrusion film line. To compensate the loss of stiffness caused by the plasticizing effect of flame retardants, 20wt% of unmodified sodium montmorillonite (Na+MMT) was added as a reinforcing filler. Flammability tests were conducted on humid and dry conditioned samples according to UL-94 and FMVSS 302 standards. It was found that PA6/PO compounds only achieved a V-2 classification, whereas the incorporation of IL-P made PA6/PO films attain a UL-94 V-0 ranking. Moreover, the two compositions pass the FMVSS 302 burning rate test. Although the addition of nanoclay made it possible to recover the initial mechanical performances, its inflammability rating deteriorated in UL-94 burning tests. In fact, the presence of clay platelets promoted the combustion of PA6/Na+MMT composites due to the hydrolysis effect initiated by the presence of hydroxyl groups on the surface of the clay lamellae. Nevertheless, the obtained data highlighted that the phosphine oxide combination with a phosphonium ionic liquid was very efficient in improving the flame resistance performance of polyamide 6 and could be transposed to design new halogen-free flame-resistant engineering plastics.