This study investigated the relationship between supplier involvement and supply chain competitiveness of fertilizer manufacturing firms in Nigeria. The research addressed the extent to which supplier involvement, influenced outcomes such as cost reduction, product quality, and responsiveness. The research designed was a correlational investigation and used the questionnaire in generating data from 35 senior staff from a population of 7 fertilizer manufacturing firms in Nigeria. A total of 3 null hypotheses were stated, with the bivariate analysis carried out using the Pearson’s Product Moment Correlation (PPMC). Evidence from the analysis showed that supplier involvement significantly influences outcomes of competitiveness. The findings revealed that supplier involvement, positively drive and contribute toward the capacity of the fertilizer manufacturing firms to reduce their costs, advance quality products, and also responsive as well. It was concluded that related actions by the management of the fertilizer manufacturing firms in Nigeria, geared toward advancing healthier and more positive involvement of their suppliers, is critical to their capacity to drive and advance their supply chain competitiveness. Hence, it was recommended that supplier involvement actions by the management of the fertilizer manufacturing firms in Nigeria build on sustainable partnerships and collaboration.