Studies show that within most countries, there are generally many different socio-cultural, ethnic and religious groups and this diversity inevitably creates a level of inter-group tension, with income disparities, cultural differences, and intergroup segregation leading in turn to social exclusion. This paper set out to develop a conceptual framework to examine the relationship between that participation and the social inclusion outcomes in the plan-making process. It addressed how social inclusion can relate to the plan-making process culturally, politically and institutionally, economically and socially with high level participation. In doing this, it adopted a case study approach using the Metropolitan Area of Abuja, the capital of Nigeria as the study sample of multi-ethnic, cultural and religious area. The research finds that participation in the plan-making process has a direct impact on social inclusion outcomes, helping to: break down cultural barriers; create intergroup cohesion; alleviate poverty; increase economic opportunities; and promote good governance. It finds that the relationship between participation and social inclusion varies across different indicators of social inclusion. It shows a very strong or moderately strong relationship across different indicators. However, the significance of relationship is very strong across all the indicators.