Inoculating cabbage (Brassica oleracea L.) plants with bio-control agents and plant growth-promoting rhizobacteria (PGPR) can considerably improve seedling quality, growth, yield, and yield-related parameters over time. An experiment was conducted to evaluate the bio-fertilizer efficiency of a bio-control agent (Trichoderma viride) alone or in combination with PGPR (Pseudomonas fluorescens). Accordingly, various seedling quality and yield parameters were studied, and the results suggested that all the co-inoculation treatments displayed beneficial effects. Still, the combination of Trichoderma viride and Pseudomonas fluorescens showed the maximum increment in all the parameters considered, i.e., seedling emergence, seedling height, stem diameter, leaf area, root length, seedling vigour index, seedling fresh weight, seedling dry weight, total chlorophyll content, plant height at 30 DAT, plant height at 60 DAT, leaf numbers, leaf area index, root length, root dry weight, number of non-wrapping leaves, number of wrapping leaves, head weight, head diameter, and head yield. The findings appear to offer a viable bio-control technique for crop protection as bio-fertilizers bundled in a single formulation.