Social exclusion is a complex concept that is relevant in terms of the health of vulnerable groups. Attempts have been made in the past to measure it, both at the population and the individual level. The aim of this research was to engage with a broad range of relevant stakeholders in Ireland in order to learn how they defined and conceptualised social exclusion. Semi-structured interviews were carried out with 24 participants selected using maximum variation sampling. One quarter of the interviewees were experts by experience. Participants included academic experts, the heads of organisations working nationally with socially excluded groups, politicians, clinicians, support workers and health service managers all with experience of working with socially excluded groups. The resulting definition of social exclusion was “the experience of lack of opportunity, or the inability to make use of available opportunities, thereby preventing full participation in society.” From this, we developed a new model of the concept comprising three elements; Opportunities, Influencing factors and Social outcomes. Opportunities are the fundamental needs that are required to be met for a person to begin leaving social exclusion. Influencing factors are a mixture of the personal characteristics and more complex problems such as the intergenerational effects of disadvantage. Social outcomes include a person being accepted by wider society, and subsequently being able to participate. The conceptual framework we developed can contribute to a better understanding of the concept of social exclusion. The traditional policy focus on improving the needs of excluded people at the Opportunities level must continue, but must be complemented by tackling the problems at the levels of the Influencing factors and Social outcomes also. In terms of changes to practice, the measurement of the social exclusion status of people engaging with primary care and other services would be an important start in order to better understand the magnitude of the work required.