The present invention relates to a process for converting the waste plastics along with the petroleum feedstock in a Catalytic Cracking Unit, in particular a Fluid Catalytic Cracking Unit employed in petroleum refineries. The invention also provides a method and hardware system to enable waste plastic to fuel conversion along with hydrocarbon catalytic cracking. The invented process aims to convert any type of waste plastic including polystyrene, polypropylene, polyethylene, metal containing Polyethylene-Polypropylene multilayer plastics & other metal containing plastics along with the petroleum derived feedstock such as vacuum gas oil, reduced crude oil, vacuum residue etc. in catalytic cracking unit.