The reinforcement of recycled polypropylene with virgin glass fibers is a widely adopted practice to enhance the mechanical properties of recycled materials. Substituting virgin glass fibers with recycled ones from authentic waste streams poses multiple challenges. This article shows a possible solution for reusing two waste fractions that count as outstandingly challenging when trying to reach a high degree of circularity. Composites consisting of a recycled polypropylene matrix derived from Austrian household waste as well as 10, 30, and 50 wt % of two different postindustrial chopped polypropylene-glass fibers (GF-PP) were produced by extrusion in a twin-screw extruder, followed by injection molding. Fiber length measurements were conducted to characterize the quality and heterogeneity of the two input GF-PP waste composites. Subsequently, the performance of these compounds was assessed by investigating their thermal, rheological, morphological, and mechanical properties. The study revealed that the initial formulation and manufacturing method of the chopped GF-PP composite exerted a significant influence on the extent of reinforcement achieved in the recycled polypropylene composites. Despite the same processing principles and parameters, the different types of GF-PP waste composites exhibited significant differences in terms of their rheological and mechanical properties. The trend was also visible when comparing the results across various compound ratios. These compounds also demonstrated acceptable flow behavior and processability. Despite substantial fiber breakage during the compounding and injection molding processes, resulting in an 87–90% reduction in the average fiber length, the produced composites displayed appropriate mechanical properties, which are mostly comparable to virgin glass-fiber-reinforced polypropylene. The findings indicate that by optimizing both the type of postindustrial GF-/PP composites added to recycled polypropylene and the blend ratio, chopped GF-PP can be effectively enhanced and converted into short-fiber-reinforced recycled polypropylene. This process serves as a model for improved recycling practices.