Aim: To examine the probability of a high sense of mastery in a population-representative sample of working-age people and to study the differences in mastery between Finnish-speaking and Swedish-speaking Finns in particular. Methods: The data originates from the Western Finland Mental Health Surveys (2008–2014). Associations between sense of mastery and language groups were analyzed with logistic regressions. Results: Swedish-speaking Finns have a higher sense of mastery and the association is mediated by social support. Moreover, a difference in a high sense of mastery is found between Swedish- and Finnish-speaking married women that are outside the labor market. Conclusions: Our findings imply that Finnish-speaking women that are outside the labor market, e.g. on maternity leave or taking care of the household, should be recognized in health and social care services as a group that can benefit from additional support.