This paper introduces a social identity perspective to job insecurity research. Worrying about becoming jobless, we argue, is detrimental because it implies an anticipated membership of a negatively evaluated group—the group of unemployed people. Job insecurity hence threatens a person's social identity as an employed person. This in turn will affect well‐being and job performance. A three‐wave survey study amongst 377 British employees supports this perspective. Persons who felt higher levels of job insecurity were more likely to report a weaker social identity as an employed person. This effect was found to be stable over time and also held against a test of reverse causality. Furthermore, social identity as an employed person influenced well‐being and in‐role job performance and mediated the effect of job insecurity on these two variables over time. Different to the expectations, social identity as an employed person and organisational proactivity were not connected. The findings deliver interesting evidence for the role of social identity as an employed person in the relationships between job insecurity and its consequences. Theoretically, this perspective illustrates the individual and group‐related nature of job insecurity and offers a novel way of connecting work situations with individual well‐being, behaviour and attitudes. Copyright © 2017 John Wiley & Sons, Ltd.