Polypropylene (PP) and polyethylene (PE) plastic waste is accumulating in the environment and the oceans at an alarming rate. The current management methods, mostly landfilling and incineration, are becoming unsustainable. In this study, thermal catalytic conversion of waste PP and PE polymers into carbon nanotubes (CNTs) using a trimetallic catalyst prepared from the nitrate salts of iron, cobalt, and molybdenum supported with calcium carbonate was reported. The yield and quality of multi-walled carbon nanotubes (MWCNTs) produced were investigated. The findings showed a high graphitic value for the CNTs obtained from PP and PE, as corroborated by the d-spacing of XRD. The ID/IG ratio of CNTS synthesized from PP and PE as carbon sources were 0.6724 and 0.9028, respectively, which showed that CNT produced from PP has more ordered graphite. The functional groups present in the produced CNTs were determined via FITR analysis. The BET and Langmuir surface areas were found to be (6.834 and 70.468 m2/g) and (6.733 and 70.347 m2/g) for CNTs obtained from PP and PE respectively. The d-spacing was computed as 0.3425 nm and 0.3442 nm for CNTs made from PP and PE. These fall within the graphite's d-spacing at 0.335 nm. The TGA showed high percentage purity of 94.71 and 94.40% for the products obtained from PP and PE, respectively. The findings showed that recycled PP and PE could be good alternative carbon sources for CNT production.