Over the last few years, transition metal based LDHs are drawing more and more attention. This is especially true for tri-metal LDHs due to their wide range of applications. This research work highlights four types of tri-metal layered double hydroxide (t-LDH) that were synthesized and used in polypropylene (PP) nanocomposites. The effect and interaction of cobalt (Co), nickel (Ni), copper (Cu) and zinc (Zn) containing MgAl LDHs in PP nanocomposite were prepared and tested. These t-LDHs (MgCoAl, MgNiAl, MgCuAl, MgZnAl) were synthesized using the urea hydrolysis method. The t-LDH/PP nanocomposites were prepared using melt mixing in a small-scale compounder. Structural and morphological analysis of t-LDH and their PP nanocomposites were done using XRD spectroscopy and SEM. The thermal behaviour of the nanocomposites was studied using DSC and TGA. Rheological analysis was done using a rheometer, flammability was analysed using limiting oxygen index (LOI) and UL94 testing. Mechanical properties were compared by a UTM and Charpy impact test. The thermal stability, flame retardancy and mechanical strength are increased with the addition of these t-LDHs. MgCuAl/PP nanocomposites showed superior thermal and mechanical properties as compared to MgAl/PP, MgCoAl/PP, MgNiAl/PP, MgZnAl/PP nanocomposites. In comparison to pure PP with the addition of only 5 wt.% of MgCuAl-LDH the degradation temperature was 43 °C higher.