This study examined the relationship between supplier relationship management and the effectiveness of firm's supply chain of selected manufacturing in Port Harcourt. Correlational survey research design was adopted for this study as this study seek to determine the relationship between the two variables. The population of this study is thirty-two (32) manufacturing companies in Rivers State which are registered with the Rivers State branch of Manufacturers Association of Nigeria (MAN). There are only 32 registered firms with MAN in the State. With regard to the respondents of the study given the strategic nature of the study, three key managers (production manager, marketing manager and logistics manager) were chosen as respondents from each using simple random sampling of the thirty-two firms constitute the study subject. This gave us a total of ninety-two (92) for the study. Structured questionnaire instrument title” Supplier relationship management and effectiveness questionnaire was developed on five-point likert scale. The result of the Cronbach's Alpha reliability test indicates .800 which is above .70 which implies that the items are reliable. Pearson product moment correlation was used to test the hypotheses using SPSS (statistical package social sciences). The study revealed that there is a significant relationship between Collaborative Supplier Relationship Management and Effectiveness of Firm's Supply Chain of selected manufacturing firms in Port Harcourt. There is a significant relationship between Transactional Supplier Relationship Management and Effectiveness of Firm's Supply Chain of selected manufacturing firms in Port Harcourt. There is a significant relationship between Strategic Supplier Relationship Management and Effectiveness of Firm's Supply Chain of selected manufacturing firms in Port Harcourt. The study concluded that Supplier Relationship Management (SRM) plays a crucial role in enhancing the effectiveness of a firm’s supply chain, particularly in the manufacturing industry. In Port Harcourt, Nigeria. The study recommended that manufacturing firms should focus on building long-term strategic partnerships with key suppliers based on trust, mutual benefit, and shared goals. This can help in aligning interests, fostering innovation, and creating a competitive advantage.