The efficacy of a wide range of multi-functional stabilisers is assessed and compared in the processing and Long-Term Heat Ageing of polypropylene. Melt flow index measurements via multi-pass single screw extrusion were undertaken, coupled with yellowness index for colour inhibition and long-term heat ageing. The outcomes provide novel information for categorising the structural activity of different stabiliser types, enabling effective processing, long-term stability, and colour. Overall, molar hydroxyl activity and sulphur content play a crucial role in melt processability, providing valuable and novel insights into their structure-melt processing interrelationship. Biphenols, aromatic amines, and one hindered amine stabiliser, Tinuvin 123, exhibited the best melt stabilisation, along with the natural antioxidant Vitamin E, displaying similar efficacy. In relation to heat ageing, there was a marked contrast in efficacy, with all the hindered amine light stabilisers exhibiting outstanding performance over the phenolic and aromatic amine stabilisers.