In applied linguistics generally and bilingualism research in particular, psychological variables remain a much under-investigated sub-category of individual differences compared with cognitive ones. To better understand the under-researched psychological effects of bilingualism, this study investigated well-being, a psychological construct, based on a big-data survey. Drawing upon a national survey (N = 12,582), we examined the influence of bilingualism (operationalised as foreign language (FL) proficiency) and 13 sociobiographical variables (e.g., socio-economic status, SES) on well-being. Among these 14 initial independent variables, perceived social fairness, SES, and health emerged as important predictors for well-being, with FL proficiency and national language (NL) proficiency as potentially important predictors; crucially, FL proficiency was more important than NL proficiency. As the first systematic attempt to link bilingualism with well-being, our study advocates (1) a more holistic perspective towards language (including NL and FL(s)) in any bilingual context and (2) fuller use of effect sizes.