This study investigated the effect of supply chain integration on the operational performance of selected manufacturing firms in Lagos State. The study adopted an exploratory cross-sectional survey research design. Dangote Flour Mills Plc, and Nestle Foods Nigeria Plc, Lagos State were purposively selected for the study, and the study’s population includes 4,007 employees of the studied firms. Three hundred and sixty-four (364) employees were selected using a simple random sampling technique. Primary data was employed and a primary instrument (selfadministered questionnaire) was designed to collect the data from the respondents. The survey data collected were analysed using descriptive statistics to achieve the mean, frequency distribution, and percentage of data collected, and inferential statistical tool (linear regression analysis) was used to test the study hypotheses with the aid of SPSS version 26. The findings of the study revealed that internal integration has a positive and a significant effect on productivity in selected food and beverages firms, supplier integration has a positive and a significant effect on quick delivery in selected food and beverages firms, and customer integration has a positive and a significant effect on customer satisfaction in selected food and beverages firms. It is therefore, concluded that supply chain integration strategies are effectively Implemented to facilitate operational performance. The study recommends that the managers of manufacturing firms should ensure that information flows between production, inventory, purchasing, marketing, and distribution units to achieve effective and efficient production and meet customer demand. Also, a high degree of reactivity and adaptability should be fostered to satisfy the demands of internal customers and optimize productivity in every department within the firm.