The existing social protection policy excludes 93 percent of the working population of Uganda's informal sector. This study sought to establish the relationship between Uganda's social protection policy and institutionalisation of informal sector workers using the institutional approach and the Subaltern theory. Sequential mixed methods design guided the study. Data from 413 participants that included informal sector workers and government and NGO staff was collected using questionnaires, Focus Group Discussions and interviews. Multi-stage, systematic sampling and purposive sampling were used to select the study participants. Content analysis was used to analyse qualitative data whereas descriptive and inferential statistics were used to analyse quantitative data. Findings revealed a significant relationship between access to social protection and formalisation of the informal sector workers as shown by the ANOVA where F=48.498 and P=0.000; and the regression analysis of β= 0.350; p= 0.000.The study revealed that a number of workers choose to work in the black market because the gains inform of social services do not commensurate with the tax contributions. As Uganda works towards achieving access to social protection for all by 2040, informal sector workers should be categorized according to industry of operation and gender and vulnerability assessment should precede policy formation to avoid further exclusion.