Polyhydroxyalkanoates (PHA) are biodegradable polyesters that can be produced in bioprocesses from renewable resources in contrast to fossil-based bio-recalcitrant polymers. Research efforts have been directed towards establishing technical feasibility in the use of mixed microbial cultures (MMC) for PHA production using residuals as feedstock, mainly consisting of industrial process effluent waters and wastewaters. In this context, PHA production can be integrated with waste and wastewater biological treatment, with concurrent benefits of resource recovery and sludge minimization. Over the past 15 years, much of the research on MMC PHA production has been performed at laboratory scale in three process elements as follows: (1) acidogenic fermentation to obtain a volatile fatty acid (VFA)-rich stream, (2) a dedicated biomass production yielding MMCs enriched with PHA-storing potential, and (3) a PHA accumulation step where (1) and (2) outputs are combined in a final biopolymer production bioprocess. This paper reviews the recent developments on MMC PHA production from synthetic and real wastewaters. The goals of the critical review are: a) to highlight the progress of the three-steps in MMC PHA production, and as well to recommend room for improvements, and b) to explore the ideas and developments of integration of PHA production within existing infrastructure of municipal and industrial wastewaters treatment. There has been much technical advancement of ideas and results in the MMC PHA rich biomass production. However, clear demonstration of production and recovery of the polymers within a context of product quality over an extended period of time, within an up-scalable commercially viable context of regional material supply, and with well-defined quality demands for specific intent of material use, is a hill that still needs to be climbed in order to truly spur on innovations for this field of research and development.