Electoral representation is a fundamental criterion for assessing the performance of democratic institutions. Since the adoption of the 2006 Constitution, the Democratic Republic of the Congo has organized four legislative elections. Yet the relationship between votes cast and parliamentary seat allocation has rarely been examined through advanced quantitative methods. This study evaluates electoral representativeness during the legislative elections of 2006, 2011, 2018 and 2023 using the Gallagher Index combined with Bayesian inference based on a Dirichlet model. Three electoral arrangements are compared: single-member districts, multi-member districts and a mixed electoral system. The findings indicate that the single-member system consistently generates the highest disproportionality, reaching a Gallagher Index of 10.68 in 2018 with a posterior probability of critical distortion equal to 0.99. Bayesian estimates further show that proportional and mixed arrangements substantially reduce discrepancies between vote shares and seat allocation. Narrow credibility intervals support the statistical robustness of the estimates. These results provide empirical evidence that reforms toward more proportional electoral arrangements could improve parliamentary representativeness and democratic legitimacy in the Democratic Republic of the Congo.