There is described a microwave pyrolysis process for the depolymerization of plastic for the production of monomers, waxes and heavy oils including the steps of: a) steam purge of the plastic from about 0.5% to about 50% w/w of a catalyst, in a media; b) pyrolysis of the plastic and the catalyst in the media with a microwave (MW) for a time sufficient to allow generation of heat providing a thermal treatment between 300° C. and 650° C. through absorption of microwaves by the catalyst and the media. The catalyst includes a compound having a high dielectric loss at the frequency of the MW to absorb microwaves, transfer heat to the plastic and initiate a pyrolysis reaction.